Hot Water Storage Tank not hot for long

rehlert

Appreciate any help and/or suggestions here.

My hot water system for my entire house consist of the following (apologize if I use the wrong terms):
Rinnai Tankless Water Heater
HTP Hot Water Storage Tank
Re-circulating line (consisting of circulator pump and timer)
Mixing Valve - I've intentionally shut-off cold water into it

My problem is in a warm basement (and even in the summer time), we don't seem to have hot water coming out of the storage tank after less than 2 hours since last usage. And so we need to run the shower for 30-45 minutes before getting the shower warm enough to use.

We even turned off the re-circulating line to test if we stopped the constant shipping of hot water out of the tank, it might allow hot water to remain in the tank long enough for comfortable showers. It did not.

I have the Rinnai maxxed out and set to 140 degrees. I have the thermostat in the HTP storage tank set to 130 degrees.

It would appear the power to the HTP storage tank thermostat and circulator pump work, because what sounds like a vibration noise (which I think is water flowing through the copper pipes) is evident when the power switch is on and goes away when the switch is off.

If I set the HTP Storage Tank thermostat to something low like 110 after just filling the tank with 140 degree water from the Rinnai for over 30 minutes, the vibration noise goes away. This leads me to believe the thermostat is working. When it knows the storage tank is hot, it stops asking for more water. But it seems like most of the time, the vibration exists.

The flow switch on the circulator pump is set to "HI" instead of "MED" or "LO".

My suspicion is once the HTP storage tank gets under 130, it starts requesting new water, but the new water going in is never hot. The Rinnai essentially just becomes a pass-through of room temperature water. So it ends up running like this for the vast majority of the day, never getting hotter, but instead eventually turning all the water in the tank cold.

The Rinnai seems to work great when a shower is turned on. I can hear the water heater kick on and I can feel how scolding hot the water from the Rinnai to the HTP is. But if a shower valve is not open, the Rinnai will not kick on.

If my suspicion as to what is going on is correct how do I make the Rinnai turn on when the tank is requesting more water? I bet if I could solve that problem, I could turn the recirculation timer back on (assuming it would also be able to kick the Rinnai on).

I've included photos to the whole setup (note the recirc timer is temporarily unplugged - I get that's not the end result I am looking for), the timer, the circulator pump, and the HTP storage tank thermostat exposed.

Thanks again!

jad3675

Does the Rinnai show any error codes when it is running?

I am slightly confused by the two pumps; I *think* it should be a sealed system between the Rinnai and the HTP with a single pump to move the cool water when the aquastat calls for it.

Also, it doesn't appear the HTP is actually plumbed into anything? The fittings on the bottom of the tank are...uh, not used? Those are for the boiler supply/return. The HTP is being used as a buffer tank, but in the worst way possible?

John

Hot_water_fan

HTP makes a high efficiency tank domestic water heater...you were so close.

Jamie Hall

Best as I can make out form the photo, I think @jad3675 may be right -- I see no way for the Rinnai to actually heat the water in the indirect. And that HTP tank is an indirect water heater, not a storage tank.
Can you make a diagram -- not photo -- of all the piping and the pumps and post that?

rehlert

Thanks for the feedback/questions.

To respond to jad3675 : No error codes. It shows it's set to 140 degrees and on. The hot water from Rinnai to HTP connects at the very bottom of the HTP. I included a photo to hopefully show that. There are two fittings that are not used at all. My guess is the HTP was designed to be served as either an indirect heater or storage tank. Those two fittings would probably be used if this was set up as an indirect heater. In this case though, it is setup as storage only. As far as I can tell, I have one of these: https://www.htproducts.com/storage-tanks.html

As Jamie Hall recommended, I drew up a diagram. See attached.

Just as a heads up to Hot_water_fan, The Rinnai was set up a year before the HTP was added. The timing was horrible, but the orginal gas burning hot water tank died and so we added the Rinnai as a more efficient replacement. But a year later, we undertook a large construction project with additional bathrooms and were told the Rinnai alone could not handle the needs.

I have to add. I am the end consumer, not the installer. So unfortunately there might have been a better approach to all this, but it was part of a much bigger (mostly successful, I might add) construction project. This was set up by a plumber my GC trusted.

Thanks again all. We appreciate the input.

Hot_water_fan

Gotcha! Yikes! I was hoping it was DIY lol.

Jamie Hall

Thanks for the diagram. As I read it, this is what happens.

Let us start from no flow. No you open a hot water faucet somewhere. Water will flow out of the top of the storage tank -- at whatever temperature the tank is holding at the moment. That water will be replaced by water from the tankless, which will have been heated by the tankless -- assuming that it switches on, which it will if the flow is high enough -- and ultimately will come from the cold water supply. You will get whatever temperature was in the tank until the tankless has had time to provide hot water to replace what you have drawn off -- basically, if the tank started cool, enough water to fill the tank.

Neither pump plays any part in this.

Now suppose the storage tank temperature is below the aquastat call. I believe that @rehlert indicated that that turns on the pump between the tankless and the storage tank. Which is fine, but as the thing is piped there's no place for the water to be pumped to, so there will be no flow (unless there is some flow through the recirculation loop) -- and the tankless shouldn't turn on, nor should there be any heat gain in the storage tank. The poor little Grundfos just sits there using power to no purpose. Fortunately they don't really mind doing that.

Now suppose instead that the recirculation pump is turned on, and there is a check valve in both it's return line and the cold water feed line. There is, isn't there? Two check valves? Hope so... Now if the recirculation flow rate is high enough the tankless should be firing whenever the recirculating temperature is below the setting on the tankless. When the tank temperature drops low enough to trip the aquastat on which turns on the other Grundfos at the bottom there, it will add to the flow rate in the recirculation line.

I suspect that with some fiddling with the controls, if the recirculating pump flow is high enough to trigger the flow control switch in the Rinnai, and if the recirculation pump is always running, the storage tank will eventually come up to whatever the Rinnai is set at. The aquastat and the pump it controls don't do anything in that scenario. An alternative would be -- again, the recirculation pump is always running. The aquastat then turns on the lower pump when the tank temperature drops to its setting, and the combined flow of the two pumps in series is enough to trip the Rinnai's flow switch. Demand from a faucet will also be enough -- provided the check valves mentioned are there -- to trip on the Rinnai.

In either scenario the recirculation pump must be running at all times.

Mind you, I think this will work with some fiddling. Is it the best way to do the job? It is, in the vernacular, a kludge. Is it the most electrically efficient? No. Is it overall the most energy efficient? No. But you should be able to set things up so at least you get hot water.

jad3675

Would it make much sense to pipe the Rinnai into the indirect as if it was a space heating boiler? That would cut down on a lot of the complexity and might need less fiddling.

mattmia2

Can you take a picture of the top of the tank and the mixing valve and how that is all connected? i don't think it is plumbed quite the way your diagram shows, i think it needs to tee off between the mixing valve and the tank somehow.

I'm thinking either the rotor in that circulator is frozen or something is stuck in that mixing valve if it really circulates through the tank through the mixing valve.

mattmia2

I don't think there are check valves because I don't see an expansion tank.

It is a bit odd and confusing and the circulator for the heater may not be piped quite right but i don't think it is terrible.

HTP makes storage tanks without the indirect coil that would be better for this purpose.

Some insulation on all of that piping would be a great idea once you get it sorted out.

mattmia2

I think when the circulator for the tank to the tankless is running it is coming out of the tank through the cold inlet of the mixing valve so with that cold supply valve to the mixing valve closed the circulation through the tankless and the tank isn't going to happen.

BillyO

you have the wrong tank for this application. you need the HTP SSU40 CB . the tappings are at different locations. You are using tank as aqua booster. Go to page 7 of HTP SSU40 CB (coil booster) install and get piping from there. I have been piping this way for 10 years, never a problem

kcopp

You shut off the cold side to the mixing valve... that will stop hot water from going through the valve.
Is it possible there is cross over somewhere in the house?

Jamie Hall

I don't see the mixing valve playing into the problem, either open or closed.

As to repiping the Rinnai, which is a tankless water heater, to serve as the heating device for the storage tank and repiping the storage tank as an indirect. Yes, that will work, too. It's still a kludge, and a poor way to use the equipment, but it has the virtue of being different.

Consider. The Rinnai is a nice tankless water heater. It is designed and intended to heat a relatively large flow of water from cold to hot while the water is running for a demand -- say a faucet or a shower -- and then shut off. A storage tank -- since that is what that HTP is being used as -- is to take a source of hot water, usually from another water heater, and store it (hence the name) to increase the volume available before the hot water runs out. An indirect is intended to take the heat from another heat source, such as a boiler, and heat hot water (and store it). The HTP could be used as in indirect. A tankless hot water heater is a miserable heat source for an indirect. Will it work? Yes. Is it the right tool for the job? No.

As I see it, there are basically two options here. One, keep the equipment which is there and come up with a kludge to make it work. It can be done either with some repiping or some rearrangement of the controls and operation. Or acknowledge that you have the wrong equipment for the job and get the right bits and do it right.

mattmia2

This once worked and stopped working, right?

Jamie Hall

mattmia2 said:

This once worked and stopped working, right?

I rather got the impression that it didn't. And, reading the OP's description and studying their diagram, I would say that it is working exactly as I would expect it to work, given the way it's piped and controlled. Um... maybe "work" isn't the right word, as that implies it's doing what's wanted. Functioning as installed and controlled. That's what I want.

mattmia2

So if it is a mixing valve without check valves it might have worked. If it is a mixing valve with check valves it would have blown off the relief valve.

mattmia2

Speaking of which, there appears to be a check valve between the tank and the relief valve.

rehlert

Thanks again all for your comments and input.

Regarding the mixing valve - as it was explained to me, the purpose of the mixing valve was to be able to mix city water with the water coming from the HTP storage tank to ensure the water to fixtures was not too hot. That logic seems to match up with the way I see it all connected. That of course, is certainly not a problem I need to worry about in my situation, so at first I turned the mixing to mostly be from the storage tank. But eventually just closed the valve on the pipe that is sending city water to the mixing valve entirely. That's what I intended to show with the "X" over that pipe in the drawn out diagram. I am quite certain the mixing valve is not involved because when the copper pipe to the mixing valve is scolding hot, the pipe out of the mixing valve is still scolding hot.

This comment is dead on correct:

Jamie Hall said:

...you open a hot water faucet somewhere. Water will flow out of the top of the storage tank -- at whatever temperature the tank is holding at the moment. That water will be replaced by water from the tankless, which will have been heated by the tankless -- assuming that it switches on, which it will if the flow is high enough -- and ultimately will come from the cold water supply. You will get whatever temperature was in the tank until the tankless has had time to provide hot water to replace what you have drawn off -- basically, if the tank started cool, enough water to fill the tank.

This matches my understanding as well.

This was extremely interesting to me:

Jamie Hall said:

Now suppose the storage tank temperature is below the aquastat call. I believe that @rehlert indicated that that turns on the pump between the tankless and the storage tank. Which is fine, but as the thing is piped there's no place for the water to be pumped to, so there will be no flow (unless there is some flow through the recirculation loop) -- and the tankless shouldn't turn on, nor should there be any heat gain in the storage tank. The poor little Grundfos just sits there using power to no purpose. Fortunately they don't really mind doing that.

I can appreciate the logic in this. I wondered how the water could move as well, and then led myself to believe flow is still happening because even though the circulation pump WITH TIMER (the one above) is not plugged in, the piping through it would just be a pass through.

Meaning this - the aquastat senses the storage tank is under 130 degrees and makes a call to the circulation pump WITH FLOW LEVER (the one below). That circulation pump WITH FLOW LEVER in turns sucks water through both the circulation pump WITH TIMER and the Rinnai water heater. Essentially, pulling water back from the recirculation return water pipes all over the house, creating a complete loop of room temperature water around the house. The Rinnai and circulation pump WITH TIMER just being pass-throughs.

Since that Rinnai is effectively just letting the loop continue all day long without ever heating the water, because no faucet or shower is opened, the water just gets cooler and cooler as the day goes on. I admit I could be wrong here. It sounds like Jamie Hall thinks when the circulation pump WITH TIMER is unplugged, the pipe in it is not a pass-through, but instead actually closed. And if that is the case, the vibrations that I can hear and feel on the pipe from the Rinnai to the circulation pump WITH FLOW LEVER could just be vibrations of the pump mechanism and not actually water flowing through. Since the copper pipes are not see through, I can't be certain, but it certainly feels like water is going through them.

So I guess one thing I am unsure of is; if the Grundfos circulation pump WITH TIMER is unplugged, does that close the pipe or just leave it open?

Jamie Hall said:

Now suppose instead that the recirculation pump is turned on, and there is a check valve in both it's return line and the cold water feed line. There is, isn't there? Two check valves? Hope so... Now if the recirculation flow rate is high enough the tankless should be firing whenever the recirculating temperature is below the setting on the tankless. When the tank temperature drops low enough to trip the aquastat on which turns on the other Grundfos at the bottom there, it will add to the flow rate in the recirculation line.

There is a single check valve 10" after the circulation pump WITH TIMER. There is also a check valve in between the city water and the junction where city water meets the recirculation line return (after the circulation pump WITH TIMER). And they are pointing the right direction. So that all seems right. I included photos showing them.

But if I turn on and plug all 3 items back in; circulation pump WITH TIMER, circulation pump WITH FLOW LEVER, aquastat/thermostat, I again start to hear and feel the vibrations in the copper pipes to and out of the Rinnai again. The vibrations that feel like water is flowing through. But, the Rinnai does not kick on.

In addition, the pipe out of the storage tank went from cool to hot, which would imply water is leaving the storage tank properly. But water back into the storage tank is lukewarm, which shows the water is not getting heated up and I think confirms that somehow the Rinnai only kicks it on when a faucet is opened and otherwise is just letting water pass through it.

Jamie Hall said:

I suspect that with some fiddling with the controls, if the recirculating pump flow is high enough to trigger the flow control switch in the Rinnai, and if the recirculation pump is always running, the storage tank will eventually come up to whatever the Rinnai is set at. The aquastat and the pump it controls don't do anything in that scenario. An alternative would be -- again, the recirculation pump is always running. The aquastat then turns on the lower pump when the tank temperature drops to its setting, and the combined flow of the two pumps in series is enough to trip the Rinnai's flow switch. Demand from a faucet will also be enough -- provided the check valves mentioned are there -- to trip on the Rinnai.

Even with both circulation pumps on and the aquastat/thermostat set to greater than 140 degrees - matching the max output of the Rinnai (also at 140), the vibrations start up and seems like there is water flow. But alas, still appears not enough to kick on the Rinnai water heater. So, unfortunately, it would appear running the circulation pumps all the time isn't going to work. But I thank you, because it was certainly worth checking. Appreciate any other ideas.

Jamie Hall

Just a bit of clarification on the pumps -- vibration does not mean that water is flowing. All it means is that the rotor is turning. Further, water will flow though the pump even if it is turned off, if it's pushed along from something else.

I would have thought that both pumps running in series would provide enough flow to trip the Rinnai on -- but that's not a given. The head loss through the Rinnai is quite high, and there may simply not be enough pump power, even with both pumps running, to get enough flow. That's what it sounds like, anyway. It was a nice idea...

I suspect that the initial intention may have been for the aquastat to turn on the pump with the flow lever -- the one I'm calling the lower pump, connected between the Rinnai "our" and the HTP "in" and that the resulting flow would be from the tank to the mixing valve, backflow through the mixing valve to the cold water supply, back to the Rinnai, on through the pump and back to the tank. That's not how the mixing valve is shown plumbed on the drawing -- and it wouldn't work anyway, unless there were no check valves on the mixing valve and it was a simple fixed set point valve. Further, if the two pumps in series don't provide enough flow, it wouldn't have worked anyway.

rehlert

More info I've found.

According to Rinnai (https://www.rinnai.us/residential/faq):
"Does a tankless water heater work differently with low-flow faucets or showerheads?
Typically you won’t notice a difference in hot water performance when you have low-flow faucets or showerheads. If you find you’re not getting the hot water you need, start by lowering the temperature setting on your tankless water heater by a couple of degrees. It’s counterintuitive, but it affects the hot/cold mix ratio and will activate the tankless water heater unit for lower-flow fixtures.

Also, remember many single-handle faucets have limit stops that affect the hot/cold mix and may need to be adjusted. If this is the case, it may be helpful to check with the manufacturer of your faucet or consult the faucet manual for details on how to make these adjustments."
AND
"What is the minimum water flow required to operate a Rinnai Tankless Water Heater?
Rinnai tankless gas water heaters need a demand of at least 0.4 to 0.6 gallons per minute of water flow through the hot side to ignite and 0.26 gallons per minute to stay in operation. If the flow rate falls below these levels, the energy-efficient Rinnai unit will turn off because it senses that hot water isn’t needed.There are several possible solutions to minimum flow rate issues. You can try lowering the temperature on the unit to avoid cutting in too much cold water; cleaning the inlet water filter on the cold water inlet of the unit to remove sediment buildup that can decrease flow; cleaning or removing the aerators from showerheads or fixtures; or replacing low-flow showerheads or fixtures. If you believe that none of these are the issue, contact your original installer or plumber to service the unit."

I tried turning the Rinnai heat setting to it's lowest at 98 degrees - no luck.

I feel like I am misinterpreting something here. If I'm reading the lower circulation pump correctly, at the highest level, I think it should be requesting .33 GPM: https://www.supplyhouse.com/Grundfos-52722518-UPS26-99BFC-3-Speed-Bronze-Circulator-Pump-1-6-HP-115-volt.

The higher circulation pump says Max flow: 8.37 US gpm, which is strange to me, since it is slightly smaller in size then the weaker circulation pump below it: https://www.supplyhouse.com/Grundfos-59896215-1-2-Sweat-UP-15-10B5-TLC-1-Speed-Bronze-Circulator-Pump-115V-1-25-HP

If the Rinnai demands at least .4 GPM, then the pump kicked off by the aquastat/thermostat never stood a chance. But I can't imagine the plumber would have installed a pump that has less GPM than a standard faucet, so I must be misinterpreting something there.

I tried to read the GPM from the Rinnai water heater directly according to the manual's instructions https://www.manualslib.com/manual/891494/Rinnai-Ruc80i.html?page=58#manual, but that setting shows "0", so that's not helpful either.

mattmia2

Perhaps the recirculation pump is moving the water through the tankless backward so it isn't tripping the flow switch.

Jamie Hall

You're misreading the scale, I think. If that three speed pump is really the UPS26-99, it's maximum flow is 33 gpm -- not 0.33. And even at a reasonable head loss through the system -- including the Rinnai -- it should be giving you 3 or 4 gpm, which should turn the Rinnai on and keep it on.

But that assumes that that pump can circulate. Which means that the recirculation piping is open -- no shut valves anywhere.

Try these tests (in all of these, I'm assuming that the diagram is accurate)

First test. Both pumps turned off. Recirculation valve (there is a valve on that line?) closed. Turn on a faucet -- any faucet. The Rinnai should kick on. If not, there may be a problem with the Rinnai.

Open the recirculating line valve.

Second test. Bring the storage tank up to temperature somehow. Then, with the recirculation valve open and the mixing valve shut off, start the three speed pump. Time how long it takes for hot water to get back to the recirculation pump. This will give you a good idea as to how much water the three speed pump is really moving.

Third test. Cool the tank off and circulate water to cool the pipes, especially give the pipe at the recirculating pump a chance to cool off. Now repeat the second test, but with the recirculating pump rather than the three speed pump. Again, this will give you a good idea for the recirculating pump's performance.

BillyO

regardless of everyones calculations, its piped wrong

Jamie Hall

BillyO said:

regardless of everyones calculations, its piped wrong

Well, yes. Not only piped wrong, but wrong equipment. But the objective of the exercise is to get something working for him. As we used to say -- improvise, adapt, and overcome.

rehlert

Jamie Hall said:

You're misreading the scale, I think. If that three speed pump is really the UPS26-99, it's maximum flow is 33 gpm -- not 0.33.

You're absolutely right. Not sure how I ended up with .33, but yeah it is 33 at max, which should certainly be enough GPM to kick on the Rinnai.

Jamie Hall said:

First test. Both pumps turned off. Recirculation valve (there is a valve on that line?) closed. Turn on a faucet -- any faucet. The Rinnai should kick on. If not, there may be a problem with the Rinnai.

Yes, there is a shutoff on the recirc line return before the first pump. I turned off both pumps and closed the valve. And yes, the Rinnai water heater went on immediately when I turned on a hot water faucet.

Jamie Hall said:

Open the recirculating line valve.

Second test. Bring the storage tank up to temperature somehow. Then, with the recirculation valve open and the mixing valve shut off, start the three speed pump. Time how long it takes for hot water to get back to the recirculation pump. This will give you a good idea as to how much water the three speed pump is really moving.

I got the storage tank super hot and opened back up the recirculation line return. Am I correct in assuming the only way I can attempt to time how long it takes to get water from the storage tank back to the recirculation pump is by trying to see how long it takes before I notice the copper pipe feeling hotter? And just so I am clear, by "Time how long it takes for hot water to get back to the recirculation pump.", you are referring to the top pump - the one with the timer, correct? If I have that understanding correct, this one was super hard to measure. After waiting 20 minutes, it still never felt nearly as hot as the (almost scolding) hot water coming out of the storage tank. But it did feel warmer than the city water after about 3-5 minutes. But again, after 20 minutes of waiting, it never got hot. Just warmer than the city water. I'm not sure, but maybe if hot water travels all the way around my house and back, it has time to cool down a lot.

Jamie Hall said:

Third test. Cool the tank off and circulate water to cool the pipes, especially give the pipe at the recirculating pump a chance to cool off. Now repeat the second test, but with the recirculating pump rather than the three speed pump. Again, this will give you a good idea for the recirculating pump's performance.

I think the only way I can cool the tank off is to turn off the Rinnai and turn on a hot water shower for about 2 hours. This would replace all the water in the tank with unheated city water. Does that sound right to you? And after I do that, the understanding is it would take hours before the third test yields warm water, because the Rinnai would need to heat the entirety of the storage tank before warm water starts to get to the pipes and then travel back to the recirculation line return. Is that your understanding?

mattmia2

rehlert said:

I got the storage tank super hot and opened back up the recirculation line return. Am I correct in assuming the only way I can attempt to time how long it takes to get water from the storage tank back to the recirculation pump is by trying to see how long it takes before I notice the copper pipe feeling hotter? And just so I am clear, by "Time how long it takes for hot water to get back to the recirculation pump.", you are referring to the top pump - the one with the timer, correct? If I have that understanding correct, this one was super hard to measure. After waiting 20 minutes, it still never felt nearly as hot as the (almost scolding) hot water coming out of the storage tank. But it did feel warmer than the city water after about 3-5 minutes. But again, after 20 minutes of waiting, it never got hot. Just warmer than the city water. I'm not sure, but maybe if hot water travels all the way around my house and back, it has time to cool down a lot.

even at like half a gallon per minute it should get almost the same temp as the outlet of the mixing valve if it is circulating. it will lose some heat but only maybe a couple degrees from the heat radiated from the piping.

Can you add the check valves and their direction on your drawing and also show the direction of the arrow on the volute of the plumps?

bidenpriece

Sediment build up in the tank

Over time, sediment can build up in the bottom of the tank, where the burner usually is. This can lead to slower heating or poor efficiency in your water heater, meaning lukewarm water rather than hot water. The solution for this is to drain the tank and to use a water softener. workforce software monday

BillyO

you have this gentleman chasing his own tail

Jamie Hall

bidenpriece said:

Sediment build up in the tank

Over time, sediment can build up in the bottom of the tank, where the burner usually is. This can lead to slower heating or poor efficiency in your water heater, meaning lukewarm water rather than hot water. The solution for this is to drain the tank and to use a water softener.

Completely irrelevant to this problem.

BillyO said:

you have this gentleman chasing his own tail

No, not really -- and I think we are well on the way to finding out part of the problem. Which was created, of course, by a misguided plumber. But that's neither here nor there. It seems clear that the intent of the design was to use the recirculation pump or the main pump -- or both -- to run water through the tankless heater and the storage tank and, when the storage tank cooled off, have enough flow to turn the Rinnai on.

Didn't work. Question is, is there anything which this poor man can do to fix the problem without spending much money to get someone in to repipe and rewire the whole thing? While I am sure that a plumber would love to "earn" the money, I'm not so sure that our OP wants to -- or needs to -- spend the money, particularly if there is no need to.

And from the dismal conclusion of test 2 up there, I'm not sure there is a cheap way to fix the problem. There simply isn't enough flow through the system. It isn't circulating, simple as that. Perhaps the reply to @mattmia2 's request will help.

rehlert

mattmia2 said:

even at like half a gallon per minute it should get almost the same temp as the outlet of the mixing valve if it is circulating. it will lose some heat but only maybe a couple degrees from the heat radiated from the piping.

Hmmm....I get that. Sounds like it is losing way more heat than expected. I wonder how. The water must be coming back, right? No fixtures are on. No water leaks. It has no where else to go, as far as I can tell.

mattmia2 said:

Can you add the check valves and their direction on your drawing and also show the direction of the arrow on the volute of the plumps?

Yes. There are 2 check valves - one bringing city water towards the Rinnai. Another one bringing recirc line return (10 inches beyond the Timer Recirc (top) pump) to the Rinnai. I enhanced the diagram to show them.
I added the direction arrows for the pumps above the pump boxes on the diagram. I also included birds eve views of the pumps incase it helps.

In case I hadn't said it before. I certainly appreciate the help on this. I don't mind the work and I'm learning a little more along the way. I has no idea what a volute was until just now.

Hot_water_fan

Would you try test 1 again for a week? To see if you even need the tank

rehlert

Hot_water_fan said:

Would you try test 1 again for a week? To see if you even need the tank

I wish! I think if we were to give up on the benefit of recirculating, we probably wouldn't need the storage tank. But unfortunately, the way it was plumbed, the hot water can't get to our pipes without going through the storage tank.

Now I find myself a slave to keeping the storage tank warm, but apparently we don't use enough hot water to do so. I actually shutdown both pumps and the aquastat/thermostat for a few days. Instead of having to run each shower for 30-45 before getting warm, we only needed to do it the first time per day. The rest of the day wasn't great, but it was fine. So we were successful maintaining hot water until the next day. But the downside is this was during summer weather and I needed to keep the Rinnai all the way up to 140 degrees. I don't think we will fare as well in the winter months. And the Rinnai apparently is not built to maintain 140 degrees. It turns out the plumber had to adjust some jumpers to get to 140. It comes out of the box with a max temperature of 120. So Rinnai says this action will burn out the water heater much faster than its normal life span.

mattmia2

Does that mixing valve have some sort of protection against either over temp output or a loss of cold supply. Look carefully at the instructions for that mixing valve, it may inhibit flow if it can't maintain the output below the set temp. I'm sort of thinking even with the cold on it reaches a point where it can't maintain mix temp and stops that circuit from circulating through the recircualtion loop and the tankless.

As it is plumbed now the only way the circulator on the aquastat can heat the tank is by circulating water

out of the tankless water heater
in to the inderct tank's tank
out of the indirect's tank through the mixing valve
out to the hot water distribution line
back through the recirculation line (water will flow through a centrifugal pump tha tis not running with a bit of restriction)
in to the tankless hot water heater

Many mixign valves have safety features to cut the flow to a trickle if the cold water is lost or if they can not maintain the outlet setpoint so the way the valve is applied may be the issue.

I think if I am looking at it right, the fix is to add a tee and a check valve between the tank and the mixing valve that then connects to the cold inlet of the tankless water heater.

Jamie Hall

Got to admit that if it were mine to play with, I'd replumb the whole thing to completely bypass the storage tank and see if the tankless would be sufficient. Depending on how one uses hot water, it might be. I'd also scrap the recirculation... but that's me.

rehlert

mattmia2 said:

Many mixign valves have safety features to cut the flow to a trickle if the cold water is lost or if they can not maintain the outlet setpoint so the way the valve is applied may be the issue.

That's interesting. But if that were the case - if the mixing valve had the safety feature cutting the flow to a trickle - wouldn't I struggle to ever get hot water flow? Why I'm asking is - if the showers in my house run for a long period of time, say 2 hours, the water will get extremely scolding hot (out of showers and faucets). In my mind that is because the storage tank is now full of 140 degree water and it is shooting that out unencumbered by any lower degree mixture.

There is a shutoff between city water and mixing valve. That shutoff is closed. It was intentionally closed so city water can't lower the temperature of the water coming from the storage tank to the hot water pipes, since in my case, my problem is never too hot water, but too cold water.

Since the shutoff from city water to the mixing valve is closed, if there was a safety feature on the mixing valve, wouldn't I struggle to get any sort of water flow from the hot side of a two handled faucets?

Unfortunately, there's not much to the instructions for this Honeywell AM-1 Series mixer (instructions attached). On the first page, it does say "There shall be no shut-off valves installed between the cold water line and the cold water connection on the AM-1 Series valve." But it never states why. And the plumber did in fact install a shut-off valve there.

I included two more photos specifically around the top of the storage tank and the mixing valve. Not sure if this is easy to make out from the photos or not. But there is no connection, except for through the mixing valve, that would allow water other than directly from the storage tank to get into the hot water supply lines through the house. So since:

1. the water from the city is closed before getting to the mixing valve
   
2. the only way to get water to the hot water supply lines is through the mixing valve
   
3. the storage tank water is going through the mixing valve
   
4. hot water taps on all faucets throughout the house are full flow
   

Wouldn't that mean the mixing valve is out of play here?

Just for kicks, I tried to follow the Valve Adjustment directions in the instructions to adjust the mixing valve. But when I loosen the screw, pull out the plastic cover, and attempt to turn valve, it is too tight to do so. Which means if I were to mess with the valve any further, I'd probably have to take it apart, following the Maintenance Procedures in the instructions. I didn't want to risk breaking it unless necessary.

And I could be thinking about this all wrong - I just don't see how the Mixing Valve is involved in my case, based on the above. Do you think it is?

rehlert

Jamie Hall said:

Got to admit that if it were mine to play with, I'd replumb the whole thing to completely bypass the storage tank and see if the tankless would be sufficient. Depending on how one uses hot water, it might be. I'd also scrap the recirculation... but that's me.

Agreed. I've done electrical and plenty of carpentry work. But this would be my first plumbing adventure; beyond installing a toilet, fixtures, and garbage disposal. So I'd probably be way above my skis with my family's only water supply.

mattmia2

I suppose it is also possible that the hydraulic resistance of that mixing valve is such what when combined with the resistance of the recirculation loop and pump and check valves that the pump sees enough head that it doesn't make enough flow to trip the flow switch in the instantaneous water heater.

BillyO

OMG

mattmia2

Which reminds me, you could have bought and installed an htp high efficiency gas water heater for what that tank, the circulators, the controls, and the labor to put it together cost.

SuperTech

A tank combined with a tankless...I never thought I would see it done. It never ceases to amaze me to see how people try to get a tankless water heater to do a boilers job. 

I think the attempt to get everything to function in its existing configuration as designed is an exercise in futility.  Even if it somehow manages to function that tankless water heater will not be long for this world.  

I'd cut out the tank and use the tankless water heater as it was intended to be used. When it eventually fails install a nice boiler to go with the indirect tank that you already have.