High water pressure

[Hastingsml]

I was getting drips from TP valve on WH. I checked house pressure 60psi. Checked expansion tank, also 60. Hot water temp 120.

I replaced TP valve. Lots of sediment in tank in TP valve (8 years old). When tank was reheating the TP valve was dripping more than old one. Checked pressure on outside spigot while WH was heating up. 140F. Turned down temp and opened hot water spigot and pressure dropped back to 60psi.

Rechecked expansion tank with no pressure in water system, 60psi. What is problem?

Why won't the expansion tank control the thermal expansion from WH? Can sediment build up in WH cause this? Is expansion tank top small? Plan to replace WH soon but would like to figure out what is happening first.

Thanks

[drainman scott]

First thing to do is drain the sediment from the tank .. it could cause your element ( assuming it's electric ) to work overtime increasing temp and pressure . you could also open and close the new TP valve a few times to see if that stops the leak .

Most water heater TP valves are rated 150 psi and 210 degree .. it seems your expansion tank is working properly and should be around a 2 gallon capacity which is the norm for a 40 gallon tank .

If you could post a pic of your WH setup it would eliminate some of the guesswork.

[Hastingsml]

It is gas WH. Since yesterday I have attached pressure gauge to WH drain to observe. It normally reads 60. When hot water is being used and WH is heating it read 55-60. When all water is shut off the WH still fires to reheat. The pressure is 60 for less than a minute then starts creeping up. When it hits 70 I barely crack a cold water faucet and it drops back down. When the gas shuts down it is 60. It is a 40 gallon tank and two gallon expansion tank. The expansion tank is mounted on a tee near the house shutoff. I don't know how long this has been like this. It seems like the two gallon is too small. I thought about hesitate switch it out for a four gallon. I plan to replace the WH very soon but don't want to have to monitor the pressure in the mean time.

[Bob D.]

Did you happen to verify that the drain cock where you attached your pressure gauge is free and clear? Many times debris will settle to bottom of tank and plug the drain. Doesn't hurt to flush it out every so often. An old washing machine hose and a 5 gallon bucket are all you need.

[drainman scott]

You could go with a larger expansion tank ... 3.2 gallon or larger ... Matter of fact a 40 gallon WH with 60 PSI it's recommended 3.2 and going larger won't hurt anything .

Do you have a close loop system ? ( a pressure reducing valve coming into the house would create one ) .

[Hastingsml]

Yes. Pressure reducing valve.

[drainman scott]

Your static pressure seems good .... When it's heating up the pressure will climb but should not exceed 80 PSI .. and your TP valve unless defective should not leak . But your HW heater is at the end of it's life cycle .

[Hastingsml]

The TP doesn't leak as long as pressure is good. I am replacing expansion tank with larger one tomorrow. Al they had was 5 gallon but it will fit ok. This is just to keep pressure under control until it is replaced. Newer system should be even better. Thanks.

[Hastingsml]

Problem solved. STUPID mistake on my part. My expansion tank is on a tee with its on ball valve shut off. When I first started figuring out why the PT valve was dripping I double checked the expansion tank and shut it off to the system. I never opened it back up. I realized it today before replacing it. Its been shut off the whole time since replacing the PT valve. With it open and the WH is fired up the pressure doesnt rise but 2 psi. Live and learn.

[drainman scott]

Glad you figured it out , we all make mistakes .

[Bob D.]

That's why safety devices like relief valves don't have isolation valves upstream by code. If they did they could be inadvertently isolated from the system rendering them useless. The same thing happened when you closed the valve to the expansion tank. But when the pressure rose with no place to go the relief valve popped off.

[AverageHomeowner]

Glad you posted back with the resolution. So often we read posts describing problems followed by suggestions, but don't hear back on how it finally turned out. It's nice to have closure and learnings.