Gas waterheater over heating with each use

[tacocat99]

Hello,

I've been having an issue with my water heater (AO SMITH) and I'm not sure if it's broken or if maybe this is just normal gas heater behavior. This is my first house and time having my own water heater. Each time I use the hot water, the temperature of the water will jump up by around 5*F. So if the water starts off at 120*F, if I was the dishes, then about 15 minutes later the temp will be 125*F. If I take a shower afterwards, the temp will be 130*F. This build up continues until it gets to 140+*F. The only thing that seems to reduce the overall water tank temperature is running the bath on full blast or not touching the hot water for about 8+ hours. If I drain the entire tank and refill it, it will heat up to 120*F and stop. Once it reaches the 120*F, it will start to overheat itself with each consecutive use.

This morning the temperature was 124*F. After taking a shower and using the washing machine on hot, the tank output temperature jumped up to 137*F. I measured the temperature at the bottom of the tank (cut off cold water and opened drain)and it was around 110*F while the top of the tank was 134*F. I had a mixing valve installed a few years ago but after about 9 months it started malfunctioning. It takes anywhere from 5 seconds to 5 minutes for the cold water to start mixing. Its also hard to set the mixing valve when the temperature fluctuates between 120 - 145*F throughout the day.

I've already replaced the gas control valve but this did nothing to fix the issue and my plumber is advising me that it would cost more to chase the problem than to just replace the water heater to solve the issue.

Is it normal for the water to get extremely hot like this or is it possible just an issue with extremely cold weather causing the cold water to heat the furnace too much? I've burned my skin rather badly a few times while doing the dishes (red mark/pain for rest of day) because of the unexpected 145*F water pouring out.

 

[Reach4]

I don't know why the WH tank temperature varies so much, but it sounds clear that your thermostatic mixing valve is not good. My expectation is that that should be fairly fast to react. This presumes that the cold water into the mixing valve is cool. I would feel that cold input pipe to check that.

 

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[tacocat99]

Sometimes it is cool, other times its as hot as the hot water line its connected to. If I run the cold water it will be cold for a bit then it will heat up to a similar temperature as the hot water line on the other side of the mixing valve.

 

[GReynolds929]

Are your uses short length and spaced close together? You could be experiencing stacking. When a hot faucet is running does the inlet pipe to the tank feel cold?

 

[Reach4]

I presume you don't have a hot water recirculation system. Do you have a thermal expansion tank near the water heater? Is the pipe upstream of that tank always cold?

Is the cold port of the mixing valve marked with a C and the hot with an H, or other way to know you have the right ports?

 

[Jeff H Young]

no this isnt normal you mention a malfunctioning mixing valve what was done to correct that ?
If water leaves the water heater sometimes 120 some times up to 140 it would be undesireable .but having a mixing valve temp will never be higher than mixing valve setting. unless as you say its malfunctioning .
get rid of malfunctioning mixing valve replace it . because it sounds bad and you already stated it is
lastly a functioning thermostatic mixer wont let temp rise above the setting downstream

 

[tacocat99]

I presume you don't have a hot water recirculation system. Do you have a thermal expansion tank near the water heater? Is the pipe upstream of that tank always cold?

Is the cold port of the mixing valve marked with a C and the hot with an H, or other way to know you have the right ports?

There is an expansion tank and the mixing valve has letter imprinted onto it that match the associated water outlet.

 

[tacocat99]

Are your uses short length and spaced close together? You could be experiencing stacking. When a hot faucet is running does the inlet pipe to the tank feel cold?

Someone mentioned this to me before. Running the washer or taking a shower seems to just make the heat go up as well. If I open up the kitchen faucet halfway and let it run, the temperature will jump from 120 -> 130 after 30 minutes (HE washer, barely uses any water, runs the hot water sporadically over 5 minutes). The only thing that tends to lower the temperature is using the bathtub on full blast or just not using the water for an extended period of time.

Is there anything I can do to prevent this issue or maybe replace the mixing valve and turn it up slightly? It would be nice if the gas water heater only heated up to the temperature I set it to, but it seems that maybe I would need an electric one that has thermostats on the top and the bottom.

 

[Fitter30]

Mixing valve is needs a new element. That big nut next to grey knob takes the valve apart. Its has a mineral build up on it. With a new element can take the old one and soak in in straight vinegar to clean it. After cleaning can just swap it out when needed. Are you also flushing the tank? Needs more than once a year.

 

[tacocat99]

Mixing valve is needs a new element. That big nut next to grey knob takes the valve apart. Its has a mineral build up on it. With a new element can take the old one and soak in in straight vinegar to clean it. After cleaning can just swap it out when needed. Are you also flushing the tank? Needs more than once a year.

About twice a year. Except for the first time I drained it (3 years after original owner installation), I haven't really seen any buildup come out. 'll try soaking the valve tomorrow to see if that clears it up. Looks extremely easy to take apart since my cold water shutoff is in front of the valve.

 

[Jeff H Young]

you really need to deterrmine . are you complaining that water exiting the water heater varies or water leaving the mixing valve varies?

 

[tacocat99]

I was wondering if it was normal for the temperature of the water to fluctuate between 120-140+ over a couple hours on the gas water heater. First time living in a house with gas appliances.

I thought it was an issue with the mixing valve at first so I turned it off, then it still kept happening. Called my plumber and he wasnt sure what the issue was and AO Smith recommended swapping out the gas valve controller. Got him to replace it and I was still having the issue so trying to figure out if the water heater isnmalfunctioning or if this temp variation was just normal.

 

[GReynolds929]

I would start with the mixing valve. As fitter says above the element can be replaced, they do fail over time. Usually the water doesn't get hot enough when they fail but the reverse can happen. Replacement should be the am-1-025rp. I have replaced multiple in the last few months.

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