Thermostatic tempering valve woes

bhowden

I have a boiler set at 160 F and the water temperature varies between 125F and 160F. To get safe domestic hot water I used a Honeywell AM101C tempering valve at the boiler. The hot water at the furthest tap was not hot enough so I replaced the valve with the Honeywell AM101 which delivers plenty of hot water. The problem I am having is that running straight hot water into the bathtub results in a warm (not hot) tub of water that I can get straight into. Running a kitchen sink partly full of water results in water too hot to put your hands in (unsafely hot). Both tub and sink are about the same distance from the tempering valve. The valve appears to work and you can adjust the temperature up and down but no one setting gives steady 110 water at both taps. Is this a common problem? Any suggestions? Could it be a flow volume issue and is there a better mixing valve to use?

Brian

Larry Weingarten

Hi, Just to be thorough and to eliminate another possible problem, try checking for a cross connection. This is done by shutting off the cold water inlet to the heater and opening a hot tap. Water should stop flowing in seconds. If it keeps running at any substantial volume, there is a cross connection to fix before playing with the tempering valve.

Yours, Larry

Ctoilman

The tub draws more water (flow rate) than the kitchen sink faucet.  If you were to slow down the tub flow rate to same as kitchen faucet (1.2 gpm) I bet the temperature would be real hot.....but painfully slow to fill the tub.  

HomerJSmith

Do you have a re-circulation pump on your sys? Do you have a check valve on the cold water supply to the indirect W/H?

EdTheHeaterMan

Although it is not stated, I assumed that Brian has a tankless coil. Homer believes he has an indirect. I also think @Ctoilman has some insight into what may be happening.

So I guess the question to @bhowden is: What kind of water heater do you have? A tankless coil in a boiler that maintains temperature, an indirect, or something else? Stay tuned for more information from Brian.

HomerJSmith

There is a limited capacity in a tankless coil. I can see where flow would be an important consideration in which case a buffer tank may be helpful. If one only turns on the hot faucet in the tub the water should be as hot as the kitchen sink. I assume that the tub is further away than the kitchen, so why is there is a mixing of cold water with the hot water at the tub?

I have seen reverse flows in a re-circulation sys. The flow of the hot input and the cold input into a proportional mixing valve has to be balanced for it to work properly.

bhowden

In this case, the boiler is actually a Sanden heat pump with an 83 gallon tank. There is no check valve between the cold input and the tank. There is no recirculation pump. There is no cross connection. Turning off the cold supply to the tank stops the hot water. I did try running the tub slower but I am not sure if it was slow enough to demonstrate anything. The water came out at the warm level. Today I did some more tests to put numbers on my description. With the tank full of hot water and the kitchen tap flowing at about 2 gallons per minute the temperature stayed at between 133 and 135F. I measured it every 5 seconds for 90 seconds with no significant change in temperature. I turned off the kitchen tap and turned on the tub tap at about 4 gallons per minute. The water temperature went to 115F quite quickly and just stayed there. I then went back to the kitchen tap and remeasured for about 40 seconds and the temperature was rock solid at 117F. The two degree difference could easily be the pipe to the kitchen sink is better insulated. The Honeywell AM101-US-1 is rated at a minimum flow of 0.5 gal per minute. It is almost like the mixing valve is stuck hot until a higher flow of water goes through and then it operates properly.

Is there a better mixing valve to use? This isn't safe the way it is now. Thanks for your thoughts so far.

Edit: To answer HomerJSmith's question, the water comes out of the tank and into the mixing valve. From the mixing valve it goes to a T and one leg goes to the kitchen and the other leg goes to the bathroom. The pipe distance is about equal.

Edit 2: So I redid the experiment of filling the tub at a low flow rate and sure enough, Ctoilman was correct and it filled the tub (slowly!) with very hot water. Took quite a bit of added cold to be able to get in. It definitely seems to be a minimum flow issue. Should I expect the valve to fail hot like this or do I have a dud? Is there a better valve to use?

Brian

HomerJSmith

What is the temp at the sink faucet in the bathroom? Is it the same as the tub temp? I assume that the tub faucet valve is all the way on the hot position in your previous post.

Does the tub valve have a temperature compensating feature? If so, what make and has it been adjusted? Some single lever tub faucets have seasonal and hot range adjustments.

If the bathroom sink temp is the same as the kitchen, then the problem is the tub valve not the Honeywell mixing valve.

bhowden

It is an old cast iron free standing tub with separate hot and cold taps (no mixing valve which is part of why it is important to get this fixed!) Yes, the bathroom sink tap mirrors the tub. When the flow is high both are high warm. When the flow is trickling both are scalding hot.

We have a second bathroom / shower with an American Standard pressure balancing valve which is interesting. Prior to this situation, once set the temperature stayed consistent as the flow adjusted up and down depending other loads in the house. Now that the temperature of the hot water is changing so does the output of the mixing valve. I had thought of it as temperature compensating but obviously it really is just pressure balancing and it ignores the temperature. I am assuming once I get the tempering valve working correctly the pressure balancing valve will go back to working properly.

Brian

Ctoilman

If I understand correctly, you got an 83 gallon hot water tank and it won't fill a tub unless the flow rate is about 2gpm (same as kitchen faucet)?  If so, that isn't right.  
Seems to me the mixing valve is working fine, it's a flow rate issue going on.  Tell me this, when the hot water temp is inadequate, what is the water temp feeding the mixing valve?  If it isn't real hot going into the mixing valve then it's sure not leaving the valve any hotter.  In other words, the mixing valve ONLY reduces temp, can not increase it.  My gut feeling the setpoint on tank temp is too low, crank it up and let the mixing valve regulate temp.

HomerJSmith

This doesn't make any sense. It's time for pictures. You are pulling cold water from somewhere, maybe tank stratification as mentioned?

bhowden

I am sorry, I must have not explained the situation very well. I will add pictures later today but the issue is that if I open the tub tap to 4 gallons per minute I get a nice 115F degree warm tub full of water (several if I want them). The issue is not inadequate hot water. The problem is that if I turn on the kitchen tap (or the tub tap) at 2 gpm or less I get 135 F scalding hot water which is dangerous. If I leave the flow at that rate it will fill the tub with water far to hot to get into.

For all of these tests the water feeding the mixing valve is between 135F and 145F. The system always delivers hot water and lots of it. Sometimes the water is too hot!

Brian

bhowden

This is a picture of the valve in question. You can ignore the temporary spaghetti of wires. They are temporary temperature sensors monitoring the system.
Brian

HomerJSmith

The Honeywell mixing valve comes with a temperature strip that can be attached to the supply water (H & C) and outlet supply and tell you the temp of the valve inputs. Does the valve have the check valves in it? Whats the temp when it flows to the kitchen and then the tub at a full flow on the hot and cold and output sides of the valve?

The only difference between the kitchen and tub is the rate of flow, it seems.

I would prefer a pic farther away of the water heater & piping arrangement.

bhowden

There is a limit to how far back I can get from the tank but this shows the cold input (pipe with pressure gauge on it) and the feed to the tank and mixing valve. Yes, the valve has check valves in it. The temperature strip shows that it is only calibrated to May 2020 so the valve I got must be old stock. The cold input to the valve is below the bottom of the scale on the strip but it is cold to touch so I would guess about 50F. The hot input to the valve looks to be about 138F. The hot water out of the valve was at about 136F at low flow and 115F at high flow.


Brian

HomerJSmith

Maybe the valve is mis-adjusted. You can remove the knob and make adjustments as to the output temp. Check the output temp at the minimum range of the knob adjustment and then at the maximum range? The knob has a stop in it and you may have to rotate the knob past the stop to reach the spool's minimum and maximum limits. What is the result? I would still like to know if the hot water supply temp to the valve remains the same at low flow and at high flow.

What is under the green flag on the wire above the hot input to the valve?

bhowden

I started this whole saga by adjusting the temperature thinking I had it too high or too low but I have not tried the high flow / low flow experiment at the ends of travel. The stops feel pretty solid and I would rather not break anything so I will leave that as a last resort. The input temperature remains the same regardless of flow. The green flag is a piece of painters masking tape that is holding on a temperature probe from some previous monitoring experiments. This morning I removed the valve and replaced it with the AM-101C that this one replaced on the assumption that a) it will test the valve vs something else and b) lukewarm water might be better than scalding hot water. I am waiting for the tank to reheat to retry the tests. One interesting note was that the check valve on the input side of the valve I took out was very slightly sticky before it opened. From that point on it worked fine (no sticking) so I doubt that is it but it was something out of the ordinary.

Brian

bhowden

Well, that appears to be the problem. With a different mixing valve installed (AM-101C) and a tank full of 140 F water the temperature at the kitchen sink (2gpm) climbed to 120F for a second or so and then fell to 115F and stayed there. The tub tap (4gpm) climbed rapidly to 115F and stayed there. Unfortunately that is the upper limit of the 101C so I either buy another 101 or live with water that is almost hot enough. Thanks all for the moral support and suggestions.

Brian

HomerJSmith

Look, you can take the knob off by unscrewing the screw in the center of the knob and pull back the knob slightly and rotating it. Then you can adjust the whole range from about 80 degs to 145 degs. Then you would have to measure the output water and adjust the valve to 120 deg.

bhowden

Yes, I understand that. The AM 101C has a temperature range of 70 to 120 but very few people seem to be able to get it all the way up to 120F (including me). When the screw is loose and the valve turns there is still a hard stop at the upper and lower end of the range. The valve that malfunctioned was the AM-101 (no C on the end) is the one that goes all the way up to 145F. The wholesaler that sold me this one is willing to replace it on warranty so all is good.

Brian