Is this Buderus DHW tank piped backwards?

Jim R.

I'm about to clean my Buderus ST-200 (53 gal) DHW tank and remembered this from a few years ago... the tank temp is set very low (110ish) even though the DHW is very hot (150+ish). I tested the aquastat and it's perfect. Also, not a big issue right now, but we barely have enough HW to take back to back 15 min showers when it's cold.

Here is a pic of how it's piped and a snippet from the manual for how it should be. I think they got the boiler water in/out mixed up. Can anyone double check for me? I suspect the aquastat isn't responding fast enough due to it's placement closer to the cold water coming in, so it's overheating. It could also explain why we're not getting enough hot water after 10-20 minutes of use.

I'm also thinking of installing a mixing valve and keeping the tank hotter (180ish), hoping to stretch out the DHW. Do you think this will make a noticible difference? We have 2 showers and eventually I'll need both of them running at the same time (4 kids) not just back to back.

Thanks.

Bob Bona_4

Yes it looks backwards, though the way it's piped now seems to obey physics-hot boiler water wants to rise naturally to return. But, as you said, the aquastat location could dictate response time. I would switch them around. What pump is driving this? It should be a Taco 008 or equivalent, or perhaps a grundfos 15/58 on high speed. Those coils present quite a pressure drop.

Yes, I would do a mixer, set tank at 140 or so, mix down to 115 or whatever your pleasure.

icesailor

The 006 controller is in the wrong tapping, according to the I/O manual you posted. Its piped backwards from what they want you to do, pipe the hot supply into the top and cool it on the way down. But with the 006 Aquastst OVER the inlet/outlet, it is controlling water higher in the tank, and if the boiler water is coming back very hot, it will effect the control. Move the control down to the lower opening where it is shown to go and it will work better.

What is the setting on the 006? With that location, the bottom of the tank can be cold and it won't respond. Connect some return circulation to the tank for DHW use and you will get better internal tank circulation.

IMO.

Jim R.

Circulator is a Grundfos 15-58 at LOW speed. I'll turn it up.

Interesting-- the two pics from the manual aren't consistent with each other. One has the aquastat above both the input/output (which is the actual setup) but first pic has it between the two. Either way, boiler output goes to the top of the coil.

One other difference from the instructions: there is no check value on the return. The 15-58 has a built in check value on the supply but I don't know why they want one on both sides.

I'm just planning to reverse the pipes in the picture. I doubt the installation company will want to hear from me 10 years later about how they goofed up.

Not sure how I'd go about adding HW re-circulation. I'm going to change the piping, up the speed, and add the mixing valve and see what that gets me.

The next size tank is 80 gal. Should I need something that big in a 2 bathroom house (we never have the dishwasher or washer going with the showers, no hot tubs, etc). Hoping to get another 10 years out of this unit!

Paul Pollets

Good luck with expecting another 10 years. I've replaced every Buderus indirect that is older than 11 years. Try a stainless tank next time. You would not need more than a 50-60g storage capacity with 2 baths...providing it's piped correctly.

Bob Bona_4

The Superbrute on low is only like a 006 Taco-not even close to needed head and flow. Crank er up to high. All these years...wow

missed that the 6006 is in the wrong tap as well. Should be in tap just below indicated boiler supply tap.

Jim R.

Paul-- Just curious, what's the reason the tanks are being replaced? Are they leaking? Not heating? Corrosion possibly due to mag rod not being plugged in?

I've heard they were very good, even on here not just from the salesman.

icesailor

What is the 006 set at?

If it is at 120 degrees, it is too low. If you are planning on keeping that tank for a while, you need to recirculate it. Even if you just put a Taco 006 B on the tank.

The circulator needs to be on the highest speed. When it is running, after 5 minutes or so, both the inlet and outlet should be hot. The inlet hotter, but the outlet hot enough so that you can't hold it.

Don't bother re-piping it. It will work fine the way it is. .

Jim R.

The aquastat is at 110 (and it's working), if that's what you're referring to. DHW is much hotter. My thinking is-- due to the pipes backward, we can't really control the temp of the DHW.

What exactly does HW re-circulation do? Moves the water around inside the tank? How often does that run, whenever it's heating? Circulation from bottom to top isn't enough? I'm not familiar with that concept at the storage tank directly. (I've seen recirc valves at far away places in houses to eliminate wasting hot water, but we don't have that)

icesailor

Jim R. said:

The aquastat is at 110 (and it's working), if that's what you're referring to. DHW is much hotter. My thinking is-- due to the pipes backward, we can't really control the temp of the DHW.

What exactly does HW re-circulation do? Moves the water around inside the tank? How often does that run, whenever it's heating? Circulation from bottom to top isn't enough? I'm not familiar with that concept at the storage tank directly. (I've seen recirc valves at far away places in houses to eliminate wasting hot water, but we don't have that)

It doesn't work that way. The 006 Aquastat controls the pump that pumps hot water from the boiler to heat the water in the tank. It is a terrible location for the control. The whole control strategy on that storage tank is bass ackwards. The controller belongs in the bottom third of the tank. Even electric water heaters, with two elements and two thermostats, run off the bottom. Depending on the size of the tank, sometimes over 90% of the time. Gas water heaters all have their gas control in the bottom 1/3 of the tank. Superstors are all in the bottom 1/3rd.

TT Indirects have a long thermostat probe that goes to near the bottom of the tank. ))^'s are rather slow acting. By the time that control acts, the water could be cold.

Bob Bona_4

If buderus wants it, do it their way. Consider Grundfos recirculation via a small pump and a diverter T under a far fixture. They work well. Google Grundfos.

icesailor

I looked at your PDF's again.

That 006 doesn't even belong on that tank and especially in that well. That well is for a return circulation pump. What belongs in the empty well below is a sensor. Like some sort of thyristor supplied by the manufacturer. It belongs connected to some sort of electronic control. Not through a line voltage switch that is wired in series through the 006 and boiler.

If you are running out of hot water, it is because the tank temperature is too low, and the controller is too high in the tank.

It was piped wrong in the beginning. If you have single lever/pressure balanced shower valves, with 110 degree hot water, they won't pass hot enough water to overcome the cold. The only thing wrong with your hot water is that the original installer didn't understand his hot water principles. And how to read a I/O manual,

Paul Pollets

Jim R: Tank corrosion or coil failure, even with anode.

hot_rod

Also, any sensor that goes into a dry well really needs some heat transfer grease. I've seen errors as high as 20 degrees with poor conduction.

icesailor

HR,

That's another issue.

The OP said he was running out of hot water trying to take two showers consecutively. What I said is my opinion on why it doesn't work as expected. The OP wanted to re-pipe the tank. IMO, it wouldn't make any difference that mattered.

I used 50 gallon tall electrics (because they were cheap) connected to oil fired hot water boilers, fired at 1.00 GPH or less, and would come home from sailing in the summer and 4 people would take consecutive showers without running out of hot water. No thermostatic mixer on the tank and standard Symmons S96- 1 or 2 shower valves. I've installed a lot of water heaters and indirects. I've never seen a tank with the controller mounted in the top 1/3 of the tank.

hot_rod

I'm with ya, not against ya on that call, Odd location for the control. Is that normal?

I thought those tanks had large diameter, 1" coils in them for low pressure drop?

Jim R.

So it's piped backwards and the aquastat's in the wrong well and it's probably going to fail soon. Ugh!

I will clean it first and see what it looks like inside before I do any other work.

Thanks for all the info. Nothing like a professional install!

icesailor

hot rod said:

I'm with ya, not against ya on that call, Odd location for the control. Is that normal?

I thought those tanks had large diameter, 1" coils in them for low pressure drop?

I never installed one like that one. I installed a Buderus tank with the boiler on top. I wasn't happy with the steel pipes welded into the end shell with the glass/porcelain coating inside. And the BST brass adapters that were leaking after three years. The woman sold the house and I was off the hook.

That was also my first experience (BAD) with a cold start boiler without any chamber and no rug on the floor. And how bad they run and smoke until they get hot. Or you put a refractory rug in the bottom to reflect the heat back into the bottom of the flame.

Jim R.

FWIW, specs on the tank say 4.3 feet of head (pressure drop) and boiler water flow rate 17.6 GPM. Specs for the Grundfos 15-58 on HI put me at about 13gpm, much closer than the 6gpm on low.

Jim R.

I think I may move the aquastat. Since I increased the speed of the pump, DHW temps are even higher than before. I think putting it in the proper place will get me better temp control. And with the boiler in/out pipes being closer to the same temp with the faster flow, I agree that repiping won't make a big difference.

Is that honeywell aquastat OK to mount sideways?

icesailor

The Honeywell 006 controls don't care how they are installed. As long as the probe is in the well, they don't care.

That lower sensing well might come out. Replace it with a standard Honeywell immersion well and just lower it down.

I'm not familiar with that tank and coil, but if the coil is as long and vast as shown on the drawings, that control may have been put that high to avoid tank overheating. If you have the 006 set at 110 degrees but are getting the 150 degree supply water temperatures, something is wrong. Everything about that top tank goes against everything I ever learned and experienced in playing with Potable water heating. Recirc. lines return to the lower 1/3/bottom of tanks. Not the top. But you're not using that tapping for a return recirculation point. What are you using for a boiler/heat source to feed the coil, and what are the controls set at?

You said that you need to clean the tank again? Why? What are you cleaning? Do you have funky water? If the boiler is running with a DHW call at 180 degrees, and you have hard water, the outside/tank side of the coil can plaque up and stop heat transfer from the boiler to the potable tank water. If you are having those kinds of issues, you need a quality thermostatic mixer installed to mix the water down to safe levels. If the coil is installed in the tank the way the drawing shows, that whole tank should be getting hot at the same time.

Jim R.

I'm going to pull out the aquastat tonight and see how it's connected. It's definitely in the wrong port. It uses a sensor bulb on a wire but I don't know what kind of thermal transfer it's seeing inside the re-circ port. The sensor well on the tank doesn't unscrew.

I'm cleaning because it's overdue (never in 10 years) and we heard from our water dept. that excess salt in the water supply could impact our heating system. Main boiler is on a closed loop so should not be an issue there. It's a Buderus G124X (74 MBTU input). One zone baseboard heat plus the DHW on priority. No idea what inside the tank looks like. I'm expecting corrosion around the coil which supposedly can be washed away by thermal shocking the hot coil with a cold stream of water.

It takes about 15 minutes of HW use (full open tap) to get the tank to start heating. From there, about 20 minutes before it heats back up (boiler water slowly warms up from 110ish to 180 and I'd say the boiler return from the tank is very close to 180 as well). Makes no sense with a thermostat at 110.

Jim R.

I tried moving the aquastat and the temperature of the DHW output was slightly better but still too hot. I had it set at 120 and was getting 145deg water. I didn't use a thermal compound but I think the connection was good. I will pick-up some, just didn't have any on hand.

Attached is a pic of the pieces I used to hold the bulb in. Do they have a name? Supposedly there's a spring that goes with them but that isn't in the bag of parts the installer left behind "for future use". I moved it back to the original location until I figure out what's going on.

In that location, aside from being too high in the tank, I don't think the well is deep enough. It bottoms out 1.5-2" before the factory well. I doubt the bulb makes it past the insulation, maybe barely.

Abracadabra

Jim R. said:

I tried moving the aquastat and the temperature of the DHW output was slightly better but still too hot. I had it set at 120 and was getting 145deg water. I didn't use a thermal compound but I think the connection was good. I will pick-up some, just didn't have any on hand.

Attached is a pic of the pieces I used to hold the bulb in. Do they have a name? Supposedly there's a spring that goes with them but that isn't in the bag of parts the installer left behind "for future use". I moved it back to the original location until I figure out what's going on.

In that location, aside from being too high in the tank, I don't think the well is deep enough. It bottoms out 1.5-2" before the factory well. I doubt the bulb makes it past the insulation, maybe barely.

Was there thermal grease in the immersion well?

Jim R.

Nope, dry as a bone.

Bob Bona_4

6006's can be pretty inaccurate so you aim for the sweet spot. The pieces in the pic are the piespacers to make up what sensors are not being used in the bundle that goes in the well. They can't be used with the 6006 bc the 6006 bulb is bigger than the buderus sensors like for their 2107 Logomatic boiler control. In non 2107 cases, I've resorted to shimming the remaining gaps around the 6006 for better thermal contact.

icesailor

That wire is a capillary tube with a bulb on the end filled with a liquid. It is NOT a wire. If it doesn't want to easily come out, don't yank it out. Spray some Kroil of something to loosen it up. If it has the silver transfer compound on it, it usually won't come out.

Where do you live to have high sodium chloride levels in your water? What else is in the water? You get white scuzz around the shower head outlet holes?

Because of the location of the 006 controller, you have an excellent example of thermal lag. Shortly after the hot water starts, the control should be sensing the temperature drop in the bottom of the tank. There is a delay in the starting of the boiler because of the pre-purge, then the boiler has to heat up. In your case, you could be running out of hot water before the boiler is all up to speed.

If you pull the 006 Well out, and it is all covered with white scale, it can be insulating the bulb from the water in the tank.

The remains of another HH.com lock-up.

The original Sparky didn't read the I/O manual. That 006 or whatever it is goes in the lower hole.

Bob Bona has the solution. You need a more accurate and sensitive control. The 006 isn't the one.

Abracadabra

Jim R. said:

Nope, dry as a bone.

It needs thermal grease to get a good reading, otherwise it'll think it's cooler than it actually is and run more making the water hotter.

icesailor

My experience with that heat transfer compound that looks like Never-seize was that if you used it, and it dried out, there was no getting the bulb out without breaking the bulb, and you couldn't get a new bulb in if you got the old one out. The electronic Honeywell has a clip to hold the sensor against the inside of the well. And you can get them out.

wogpa67

He could use a Ranco digital setpoint control. They are inexpensive, adjustable differential and reliable. He could use the spacers he has to get good contact in the well.

Bob Bona_4

My experience too with the "heat transfer compound". Say goodbye to the bulb bc it's cemented in the well for all eternity. What fun!

Abracadabra

I've never had an issue with removing a bulb with thermal grease in the well. Never. Does it get tricky sometimes to get the old one out? Sure.. Last week I had to pull an old aquastat out. According to the date the tank was installed, that aquastat was in there for 14 years. If you are pulling the bulb, it's usually because there's a problem with the aquastat, so no big deal if you destroy the old bulb.

Mark Eatherton

Welcome to the world of thermal stacking. I've seen 20 degrees F difference from stat settings to tank outlet due to this normal condition. Definitely add a mixing valve, and move the stat to the lower available tapping. It will help, but you can still expect shortages.

If connected to a high mass cast iron boiler, it gets even worse in the summer when the boiler is allowed to do a completely cold start. By the time you get the mass of the boiler up to temp and start discharging water temps high enough to transfer energy from the source to the load, you are already running out of hot water.

One possible fix is to put a timer on the boilers TT contacts, and fire it 10 minutes before the first DHW load comes on line. That way the mass of the boiler is already hot and ready to rock. This applies to high mass cast iron boilers only.

You can NOT do this with a low mass boiler (never fire a low mass boiler without circulation unless you want your sphincter to do the momba...)

If you have to replace it, I'd consider using the Turbomax reverse indirect. One of the highest transfer rates of any DHW generators out there, including the TT tank within a tank design.

I believe Mr Holohan has one in his house, and he had a house full of women at one time, and if anyone was going to run out of hot water, it would have been him.

ME

icesailor

The fastest way to end thermal stacking is through recirculation.

You can even solve it by putting a small bronze circulator between the hot supply outlet and the cold inlet. Oil fired water heaters are especially prone to this.

That tank particularly sucks because there aren't enough tapping's in it to control the inlet.

I've seen oil fired water heaters with 180 degree water at the top, and sandwiched hot to cooler water down to the control where the control is set to ii0 degrees and the burner isn't running. That is especially a problem in restaurants where they have many, many small draws.

icesailor

Abracadabra said:

I've never had an issue with removing a bulb with thermal grease in the well. Never. Does it get tricky sometimes to get the old one out? Sure.. Last week I had to pull an old aquastat out. According to the date the tank was installed, that aquastat was in there for 14 years. If you are pulling the bulb, it's usually because there's a problem with the aquastat, so no big deal if you destroy the old bulb.

That's because you had a spare bulb that fits when you broke it off. And my supplier never stocked the one that fit, but 6 of the ones that didn't fit.

Jim R.

FIrst, thanks again to everyone who has chimed in. This has been a very educational experience for me and all comments are appreciated.

So today I did the dreaded tank cleaning. I expected to see mountains of sediment like I've seen in some old hot water heaters left for recycling. But all I saw was Buderus Blue! There was a light coating of "mud" at the bottom but it washed off easily. Here are a few of the pics before cleaning. I didn't get any when I was done (wife was hurrying me up) but it looked new. I was very surprised after 10years.

But it's not all good news. Look at how thin the anode is. Isn't this supposed to be 3/4 - 1" thick? It's like 14 guage wire. I can replace this easily without draining the tank again. Just have to figure out the part# since Buderus won't tell me. Still, the anode status light is green.

Also in the pics... see the hole near the top? That's where the aquastat is currently. The well doesn't even make it into the tank. So that's why I'm getting a bad readout.

I have to figure out how to mount the aquastat to the lower port (correct port) without rigging it. The lip on the well is about 1/2" but on the buderus well it's 3/4"wide and the aquastat won't clip on.

I upped the temp to 140 on the aquastat, so probably 190 degree water will come out. Boiler is running for 1hr and only at 180 deg. I will leave it like this for a few hours to kill any bacteria before I turn it down.

Going to the depot to see what I can attach the aquastat with when I move it... I will update.

Jim R.

Aquastat at 140 trips the PRV (I was watching closely). Bumped back down to 110. DHW is steaming HOT.

RobG

Can we see some more pictures of the system? Other than moving the sensor it's possible that the installer of the pump simply installed it backwards. Need to see the piping to find out though are there check valves in the domestic piping?

icesailor

Do you have the original installation manual for that tank?

Here is the current one for the tank. That Honeywell 006 control is in the wrong location and on page 7, the instructions are there for hot it is supposed to be connected. It belongs in the lower hole/ Spark or someone installed it in the wrong place.

http://www.bosch-climate.us/files/201307082105550.7747001883_ST150-ST300InstallManual0906.pdf

In one of your posted photos, there is a hole above the indirect coil. That is for the return circulation to enter the tank. It looks like the 006 just screws through the jacket.

Bob Bona_4

6006 is reading way off. Pasco makes great temp gauges that fit in a well you solder into a tee on the hot side of the domestic. Then you aren't driving blind. Then, Caleffi makes a sweet mixer with the same temp gage arrangement
on it's mix outlet. This is on my own system- Triangle Tube Smart 80 with a TT Prestige 110 boiler.

icesailor

Bob Bona said:

6006 is reading way off. Pasco makes great temp gauges that fit in a well you solder into a tee on the hot side of the domestic. Then you aren't driving blind. Then, Caleffi makes a sweet mixer with the same temp gage arrangement

on it's mix outlet.

Are we talking two different things?

The manual for that tank has specific instructions for connecting what they provide to connect to a Logmatic control. It goes into the lower hole. It appears to have a ridge for a locking clip to hold the probes in place. Someone posted a photo of the probes. Farther along in the instructions, they give specific instructions for installing a 6006 Honeywell. That goes in the same hole. As Bosch/Buderus shows the installation, it must go what some would consider as upside down.

There may be a lot of better controls out there than a 6006. But that is what is there. Its easy to move. It still needs a mixer and it will still stack like stack of fresh cooked pancakes.