water heater issue

Brad White_9

the relief valve is a T&P works on temperature and pressure. Unlikely but eliminate that as a variable.

reggie

I recently replaced my water heater and I am experiencing blow off periodiaclly from the pressure relief. I did install a 4.4 gal expansion tank as well as a check valve between the tank and the shut off valve but the problem persists. I have a 40 gal tank and my house pressure is 60#. Any ideas or suggestions?

Plumdog_2

Check valve?

Make sure the expansion tank is between the check valve and the water heater and is oriented in the correct direction. If your house has a Pressure Reducing valve on the Water Service it may be failing; allowing the pressure to exceed safe levels.

ed wallace

relief vavle

make sure relief valve is a t and p vavle rated for 150 lbs typically its a watts Xl 100 t nd p vavle

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reggie

Thank you. I did verify the house pressure after the pressure reducing valve. I left my pressure gauge on for about 1/2 hour and there was no rise at all. Also the reducing valve has also been replaced. The expansion tank is between the check valve and the water heater and the check valve is in the correct flow position. I have not taken a temperature reading but the thermostat is set at just below the warm setting. Any other ideas?

Gene_3

test the temp

with an accurate thermometer at the closest faucet, carefully, be sure it is not overheating, the T&P may just be doing it's job which to release and keep the tank from exploding, yes exploding.

If it is near 200F something is wrong. Shut it down and call a pro.

If it is just over 120 lower it to 120, it may solve your problem but it will save you money.

Phil Burkhart

Most thermal expansion tanks come with a factory precharge of 40 PSI. If you have 60 PSI system pressure the bladder or diaphragm will expand as soon as you pressurize the system. Now you don't have enough volume for when the water expands when the burner comes on.
You must remove the tank from the system and add pressure to the tank to match your system pressure.
There can be no valves, check or shutoff, between the expansion tank and the water heater.

Brad White_9

Or

you may not have to remove the tank, there may be a Schraeder valve (bicycle tire type valve) for charging the dry side of the tank. It may have a nitrogen charge so you may want to boost it with only dry nitrogen to be consistent. If air, so long as it is dry though, I do not see it as a big issue.

My $0.02

Gene_3

T&P's

are rated to blow off at either 150psi, 210*F or both. If your valve is releasing at least one of those conditions is being met, it could also get a sudden shock from water hammer, over expansion of water when heated , or the valve is ng as well.

Test the temp and pressure, you can fashion a simple pressure tester from the hardware store using a gage that reads up to 200psi and a fitting that attaches that to a female hose fitting, attach to your drain valve and read pressure.

You may also be experiencing what is known as "STACKING". It is possible to create a condition inside the water heater, usually by drawing small amounts of hot water in sucession, where there are distinct levels of temp going from the bottom up every couple of inches so the bottom could be 100 then 110, 120, 130 , 150 etc to where the very top is over 210*F.

The only cure I know for this is to shut the heater down and let it cool, lower the tstat so you only get 120 and restart and avoid " as much as possible" drawing little bits of hot water all day.

Measuring the temp right at output may expose this.

Larry Weingarten

check valve

Hello: It is likely the check valve is the source of the problem. Why do you need it? Normally a little thermal expansion back into the cold side is not a problem.

Yours, Larry

Gene_3

good point

the check valve could be trapping built up pressure in the tank, shouldn't be there

if you want a thermal trap to keep h/w in the tank and be more eff you just run the hot up from the tank, over to the side then down 12" and back up to the piping, it keeps heat from rising while not using h/w.

rick in Alaska

p&t

I would put a pressure gauge on the water heater and fire up the heater. If the relief valve starts leaking and the pressure is below it's rating, and the temperature is not up to 210, change the relief valve. It is possible to get a bad one.
GOOD LUCK. Rick in Alaska