Domestic Hot Water Temperature Issue

Doug83 · April 2018

Okay- I think this may the only place to get accurate direction on for this problem.... Some of you may remember I recently replaced a 45 year old atmospheric boiler/w hot water coil ( I also have a back up hot water heater/and summer use) with an HB Smith 520K gas fired /power burner. They also installed a higher end type mixing board panel with a controller (see pics), mixing valve and recirculating pump. To be honest, I am not sure there was a circulating pump before....Here is what I do know. We never had a hot water temperature issue before. No one ever complained about it, and I lived in the 5 apartment building for several years myself. The controller is set for 130 degree output, and I am quite sure that every time I saw the actual output, it was pretty darn close to 130 degrees. The new installation was in place in October 2017. This building is five apartments with one bath and one kitchen in each apartment.
A few months ago, the actuator on the mixing valve failed, and while the tech was there to replace the unit, we saw a spike in pressure to over 100psi ( it pegged the 100psi gauge). It must have been under 125 psi or the relief valves would have let go. It came back in short order to 50 psi, which is the set point of a cold water booster pump we installed a decade ago. No one could understand why we had that pressure spike, or remember if it was there from the beginning. I immediately installed an expansion tank, and had not seen the spike since. A few days ago, one of tenants said that the hot water was changing from extremely hot, to lukewarm in a matter of a minute or two and made showering very difficult. This is the first time I heard someone say this..although after talking to some other tenants they said it started after the installation of the boiler and just thought that was the new system ( I should have never moved out of the building). A tech came in and spent all day trying to reprogram the controller...we used tons of gas and water... the controller could not come close to maintaining the 130 degree set point and would swing from 160 degrees to 90.... We saw that it appeared the recirculation line temperature was culprit. It makes sense, the hot water was relatively fixed, the cold was fixed and the only other water mixing with the cold water inlet to the mixing valve was the recirculation water. After 6 hours of that troubleshooting, I said let's stop, let me put the back up hot water heater on and try to understand what is happening here. I put the back up hot water heater on, and I was happy to find that the shower water was now relatively constant. The output of the hot water heater was 130 to 140 degrees, and showering was perfect. Here is the rub! The sink line, the farthest riser from the boiler room and hot water heater, wouldn't get full hot water.... It would go to 110 degrees, and then slowly drop to 86 degrees, in almost every apartment plus or minus a degree or two. I decided that the next step would be to shut the hot and cold water valves at every sink thin king that maybe cold water was passing through the faucets. I left the third floor apartment hot water valve open, and then ran the water. it did the same thing! This was crazy to me... I then traced the hot water outlet from the heater in the basement and measured 140 degrees as far as i could go before it disappeared into the ceiling. I have a few panel doors I could open after that so I could see where the first floor kitchen sink hot water was coming from. It was luke warm as well. I now want to find the exact location it taps from on the hot water line and see what is going on, although I am not sure I will find the answer. Here are my questions... Do you think we solved the problem that the sink line is the contributing issue to the recirculating water? What is strange to my is that the bath line was doing this before too with the new system...but now, not with the hot water heater. What is out of the picture is the mixing valve, and the new recirculating pump which I am pretty sure I never had before. Could this be a pressure issue with the booster pump pumping cold water into the recirc line?? I never had the problem before though...Could the high pressure condition have caused a check valve to fail? If so, how the heck will I ever find that valve.... Your incredible experience will at least give me some insight as to what to look for next... Thanks all!!

Jamie Hall · April 2018

Just to help me get my head around this -- when you mention the output temperature from the mixing valve swings, the question is -- how fast? I'm a little concerned about the time delay in the control loop from the sensor to the mixing valve and the mixing valve's actuator, particularly at lower flows.

Also, I assume you did this but refresh my memory here -- does it do the same thing with the recirc . pump shut off and the valves closed to isolate the recirc. line?

Doug83 · April 2018

@Jamie Hall , Jamie, The swing when the new mixing valve panel was troubleshot two days ago was a continuous movement in either direction over say 4 minutes , 2 up, then 2 down. This is under load conditions ( two hot water faucets were open). The tech said that the controller PID settings looked wacky ( maybe there was something that caused it to change settings) but the target temp of 130 was still in place... so... then he started adjusting trying different PID setting and would get the range down to say 30 or 40 degrees. He tried throttling the valves on that panel in the picture....but I kept telling him... " Listen- here is what we know, no one ever complained about swings in temperature before, and I never had this problem when the last boiler was in operation, so something changed..."
IN fact, I installed a wifi temperature system on my hot water system after the first actuator failed on the mixing valve. See the attached charts. Even though some of the tenants said there were historic swings in temperature ( who knows!) this chart shows something different. The chart that looks stable on the left and then crazy upswing, and then stable on the right is the first 28 days of the last 31, then the 29th and 30th show the crazy swings, and then the 31st shows when i put the back up water heater in. The other chart shows a 24 hour period of the crazy swings and then stability range with back up water heater.

I asked him if we can cut out the recirc line, he said that that is important for tempering the cold water ( they mix) into the mixing valve, it also goes to the boiler to mix again with the cold ( see drawing) . He said we would damage the mixing valve if we cut out the recirc line.... I don't know if that is true but can understand.... I told him at the end ( this was the contractors start up guy, not the sub that builds the boards and is an expert on the board controls) that I wanted to put the back up water heater on, and then get the sub who built the board in. They want to come, but I wanted to run those tests i mentioned on the kitchen sinks first... I am so confused as to how this is happening. I really want to trace the hot water header to that first floor hot water line to the sink to see what is happening.

hot_rod · April 2018

There is a specific way that recirculation pumps tie into some mixing valves. if the valve does not have the ability to shut off the H port 100% "bubble free" then the valve can creep. As in temperature.

A small portion of the recirc needs to go back thru the valve. Just enough to overcome the temperature drop in the recirc loop. The rest needs to go back into the tank or source. A balance valve needs to be installed to adjust that ratio under no draw condition. looks like this drawing below.

I'm not saying for sure that valve needs the bypass, depends on the build of the valve. The installation manual should indicate and explain that bypass, if needed? A globe or balance valve, not ball valve for that adjustment.

Looks like someone has been trying to choke down valves for some reason?

Doug83 · April 2018

@hot rod ,thank you, I have to ask the designer of the board about the 100% shut off. We definitely do not have the circuit you are showing in the drawing, I need to ask about this as well. I am also wondering if there may be a failure of a check valve in the recirc line such that cold water is entering the recirc line under a higher pressure from the cold water booster pump, and then mixing with the hot water ( hence the 85 degrees ). I think a good test for me to try today is to shut the recirc line off at the hot water heater ( when it is no in demand) and see if I get straight hot water out of the hot side of the faucets.

hot_rod · April 2018

Two things can happen with an improperly piped recirc to a mix valve.

Temperature can creep during periods of non use where the valve does not see cold water to regulate accurately. Or it can droop below setpoint.

An oversized recirc pump can actually backseat a check and prevent cold from entering. The delta P of the high head circ adds to the incoming pressure and prevents the check from opening properly and allowing cold to enter and blend.

We talked a bit about recirc piping and problems in Idronics 11.

Here is a piping schematic we suggest for the Caleffi EMV electronic mixing valve, LegioMix.

A DHW expansion tank is also required when you check the incoming water line.

Doug83 · April 2018

@hot rod , I think we solved two problems here! I am pretty sure your analysis is what we are going to find happened when the new mixing valve board is placed back in service. That circuit, along with the cold water booster pump on the inlet needs to be properly designed and balanced. The best case testing would have flow meters, pressure gauges and temperature gauges on the system. The only thing I am missing is a strap on flow meter.
What was perplexing to me, is that when I valved out the boiler coil and mixing valve panel, and placed the old back up hot water heater in, I was having the same problem, but only the sink line, not the bath line. Today, while the water heater was under static conditions , I valved out the recirc line that is connected to the cold water inlet of the tank. That recirc line has a check valve on it right before it enters the cold line. I then went to the first floor and ran the sinks hot water line ( remember, I have a cold water booster pump at 55 psi pushing water around here) , I was praying I would see a change and I did! The water temp started at 75 degrees, then climbed to 130 + and stayed there, no oscillations! I am going to have to guess that the check valve was blown out when we had 100 plus psi conditions on the water system when they installed the mixing valve board. Now, I have to call the board designer and plumbers in to look at their installation against your analysis. When I valve out the water heater, I valve out the recirc check valve that I just found to be an issue, so the problem we had when the new board is in operation is probably related to what you indicated, or, also , another check valve blown somewhere on that line....Thank you for your help

hot_rod · April 2018

Is there a thermal expansion tank in the system, you need one when check valves are placed in the piping.

Doug83 · April 2018

@hot rod , there was no thermal expansion tank installed for 4 months of operation until I learned that one should be in place from posting on this wall.
One question I have is , is it obvious that since cold water is getting into the recirc line , that the check valve in that line is bad, and that maybe since the point where the check valve and the cold water lines interface, we have a pressure issue? The cold water at those points is a straight up 55 psi, the set point of my domestic water booster pump. If the recirc line comes from the top floor , after running through the whole system, maybe all we have left is head pressure plus, but not enough to overcome the 55psi cold water line. The recirc pump they installed maybe adds 8 or 10 feet of pressure .

hot_rod · April 2018

Gosh, if you had PT ports in a bunch of locations you could chase down the pressure question. PT ports are a simple inexpensive way to check pressure and temperature, and use the same gauge for accuracy.

Typical brass swing checks are not 100% shutoff, so it could have enough leak-by?
Also swing checks need a pressure differential to close at all. If pressure is the same on both sides the flapper floats or just closes some from its weight.
My opinion is swing checks are good for sump pumps, sewer pumps, well pumps, air compressors, etc. Any application where the down stream pressure is greater when flow is stopped. A spring assist disc check is a better choice often times, if you cannot assure ∆P.

Also with swing checks the Cv is in the fully open position. If in-adequate flow is passing thru, the flapper may rattle or be in a partially open position.

Doug83 · April 2018

@hot rod , I think I just listened to a presentation by John Siegenthaler for Caleffi, and you were the host??? How many hot rods could there be...? Amazing presentation. I didn't know you were a guru too! But it may have been obvious from your comments..I think this presentation was when Idronics 21 was just coming out. Just a note on my system after listening to the presentation, we have no balancing valves in my system, and no glove valves for adjusting flows... Every valve is a ball valve, and the contractor just installed a board he had sitting around... It was not engineered to work with my system. The original boiler engineering group and the contractor are now working together to hopefully resolve my issue... I wish I knew what I had in my old 45 year old system before they dismantled it. I am sure it was simple... and for as simple as it was, it worked wonderfully... I love that these presentations are all on U Tube. Thanks again for your help.

hot_rod · April 2018

And thank you for the nice comments.

Often times balancing valves are thought of as a costly, frivolous extra. That is until you need them to set or confirm flow or troubleshoot.

There are quite a few choices when you select balancing devices, most hydronic specific engineers have experience with sizing and selecting. Good to get the contractor and engineer working together, there can be a bit of math involved when designing and selecting valves.

You will need low lead valves also in potable water installations.

Yes, webinars and You Tube have changed the training landscape. We generally get 600 or more attendees at the monthly Coffee with Caleffi. You can reach a lot more folks online compared to in person training.

Doug83 · April 2018

@hot rod , Bob, question on design while I wait for a solution to my recirc line going warm to hot... the old atmospheric boiler ( before the HB smith /power burner) had a Watts Regulator N170-M2, with no circulator. Unfortunately I don’t have perfect pictures, but it looks like they fed the recirc line into the cold, and that , I think split between the Watts and the boiler coil.

I’m just thinking ahead here , in case they run into a problem. I think they are going to recommend a thermostatic valve similar to what was there, and remove the controller and mixing valve. The guy who designed the system said he was told this was a 13 unit building, but it’s only 5.... I know it’s not the most efficient , but if they change the current valve back to a thermostatic and install globe valves to adjust flow, with like 80 or 90% of the water going to the boiler coil and say only 10 or 20% to the cold water going to the thermostatic valve, can you think of any downsides to that, other than having to use more hot boiler coil water? I’m assuming they may also take the circ pump out too since that was the previous design as well.
Thanks for your thoughts

Domestic Hot Water Temperature Issue

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