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hot water pressure relief valve

October 04, 2014, 02:57:06 pm

I am camping this weekend and my relief valve went off. Since it is 20 years old, I decided to replace it. Very easy job. My question is what temp. Should the water be? The valve range is 140-210 degees. The thermostdt is pre-set at 140. My water feels alot hoter. But I have no way to measure. Any advice would be apprieciated.

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Re: hot water pressure relief valve

Reply #1 – October 04, 2014, 03:06:38 pm

Very Unusual that the temp/pressure relief valve would need replacing.
Usually what happens is that water in Hot Water tank cools and expands and opens the pressure relief valve.  Usually due to loss of air space in tank.
Drain the tank, close drain and turn pump back on.
If this does not work look to the accumulator, if diaphragm is not doing its job pressure will build in tank and pressure relief valve will open.
Temperature on these water heaters is not settable unless the thermostat has been replaced by an adjustable one.
Gary B

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Re: hot water pressure relief valve

Reply #2 – October 04, 2014, 03:15:51 pm

Hi Gary thanks for the quick response. I was going to drain tank and and try with the existing relief valve but since I'm at lazy days camping replacing the valve while draining the tank seemed to be the thing to do, since I have no way to measure temp. And maybe after twenty years the valve is bad. Replaced valve drained tank, refilled and startedbup heater, so far everything is fine. Will measure temp when I get home. If to hot will replace thermostadt.

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Re: hot water pressure relief valve

Reply #3 – October 04, 2014, 08:12:12 pm

I've also had to replace a T&P valve due to deposits (calcium, etc.) causing it to not seal tightly, allowing a light drip. 

My old Atwood manual says water temp should be ~140F.  I have noticed that my T&P valve would occasionally open when heating a full tank of cold water and that the thermal expansion would stay under control if I kept the hot water heater on all of the time. 

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Re: hot water pressure relief valve

Reply #4 – October 05, 2014, 07:44:19 am

Hey Robert I managed to find a meat thermometer and held it under the faucet. 140 right on the button all is well. Thank you.

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Re: hot water pressure relief valve

Reply #5 – October 05, 2014, 01:20:26 pm

Water heater safety valves are designed to pop off if either the pressure or temperature is too high. When they get old they can fail in the open or closed position. If it fails by sticking closed it's no longer providing any protection and in theory a pipe or the water heater itself could burst if the operating limit control or gas valve fails and the temperature / pressure gets too high. If it fails by sticking open or dripping you'll have water all over the place. Sometimes they get rust, dirt, or calcium deposits on the valve seat that cause the valve to fail. If it fails and you don't have a replacement valve, stand clear so you won't get burned by the hot water and suddenly pop the little lever open and closed repeatedly to see if you can dislodge the deposits from the valve seat. This works temporarily a lot of the time, but you'll still have to replace the valve as soon as you can. If that doesn't work and you're in the middle of nowhere without a valve, let the water heater cool down, take the valve out, try to hold the valve open and scrape or otherwise dislodge the deposits with a small tool, then try to blast water inside while holding the valve open to wash out the deposits you just scraped out. I think soaking it in vinegar can sometimes help too... Ultimately the best solution is to replace the valve so plan on doing that as soon as possible... Those of you reading this who don't have a problem with your water heater's safety valve, DON'T mess with that little lever. If your valve is working now and you open it and some debris gets stuck under the valve seat you'll cause the problem that started this thread in the first place, just saying.

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