View Full Version : Water Heater pressure

11-30-2004, 11:59 AM
Thank you one and all for the assistance in solving this problem. The cure was to replace the expansion tank. Pressure is now 60 lbs and topping out at 65 when the water heater kicks in. The old expansion tank had a ruptured diaphram and all air had leaked out. Original text describing problem is shown below. Thank again. David

We are experiencing intermittent rises in water pressure and am suspecting the water heater gas valve.

We noticed the water heater temperature/pressure relief valve venting so I replace that. The problem continued. I attached a water pressure gauge at the drain valve. The gauge has a high point needle and while the pressure read 60 psi at the time it showed 60 again the next morning but also indicated that it had gotten up to 160 psi had been reached during the night. Water company came out and tested and said there was 102 psi at the main line (before our regulator). We put in a new regulator, set it to 60 psi and again the next morning it showed 60 but a peak of 160 during the night. We had put a bucket to catch any water passing through the relief valve and water is present there.

I did turn up the temperature on the tank and it heated and shut off. I did that a second time and again it heated and shut off (no water passing through the relief valve either time nor a rise in water pressure.

My question is: Will a heater gas valve perform OK sometimes and then go wild and not shut off? This would overheat the water causing excessive pressure. However, wouldn’t the water pressure vent itself back into the street main at pressures over the 60 that the regulator is set at? There is no check valve that I am aware of in the system between the heater and the street main.


11-30-2004, 02:19 PM
With a pressure reduction valve, you may want to consider an expansion tank. The reduction valve acts as a one-way valve. If you use a lot of hot water, the cold water comes in, fills the tank, gets heated, expands, and can't go anywhere - thus your pressure goes up until someone opens up a tap, then it goes back to "normal" (especially if you don't use much which could cause the whole thing to happen again). Without a pressure reduction valve, that expansion can go back out against the main and never really show an increase in the house.

The expansion tank acts like a buffer, preventing excessive pressure.

My opinion of what is happening.

11-30-2004, 02:52 PM
We do have an expansion tank or I think that is what it is. About a foot away from the hot water outlet on the heater tank is a blue tank about 2.5 gallons in size that has a rubber bladder in it. It was installed to prevent water hammering. Does this work as an expansion tank as well?

This pressure build up just started about a week ago. Nothing has been changed in the system for about 5 years now so something that was working has now become faulty. Relief valve and pressure regulator has been replaced. Maybe I should check blue tank. Maybe the bladder has ruptured and no longer buffers. Then again we don't have hammering either.

I should add that there is a hot water circulating pump in the system as well but doubt that it would affect pressure as it merely takes water out of the tank at the top and pumps it back into the bottom.


11-30-2004, 03:40 PM
Rap on the expansion tank to check to see if it is full of water. It should sound hollow at the top and filled at the bottom. It could have a failed bladder and be full of water. Also, you could check to see if it lost its charge in the bladder. Turn off the main supply line, then turn on a water tap until no more water comes out of the faucet. Then, using an automotive tire air pressure guage, check the pressure on the tank. Don't remember what the nominal pressure should be, it may be on the tank. If it reads below that value try to fill it up. Close the faucet you turned on, open the main valve and see if the expansion tank fills up again. If so, replace it. It is usually a very simple thing - using some pipe dope and or teflon tape on the new threads unscrew the old one after turning off the water and screw in a new one. You usually don't need any tools as you have a fair amount of leverage with the size of the tank; if not, then a strap wrench may be needed.

11-30-2004, 04:25 PM
"We do have an expansion tank or I think that is what it is. About a foot away from the hot water outlet on the heater tank"

The thermal expansion tank should be installed on the cold water feed line to the water heater as per manufacturers instructions.
Also, I'm thinking there might be a check valve somewhere (next to the recirc. pump or next to the water meter?) which would make it a closed system causing the T & P to release or the pressure regulator valve, (PRV) doesn't have a built-in by pass feature which the better models do.

If the Water Depts test is accurate and there is only 102 P.S.I. incoming then the 160 P.S.I. created overnight would bleed back into the incoming water service piping.

11-30-2004, 07:40 PM
Installing the exp. tank on the hot outlet probably shortened the life of the bladder.

He may have a non-bypass PRV which explains how the pressure builds all the way up to 160.

12-02-2004, 04:44 PM
The expansion tank was the problem. Replace it and all is working great again. Pressure is 60 lbs. with a maximum of 65 when the water heater kicks in. Old expansion tank diaphram had a hole in it so ceased working corrrectly. And I was in error in stating that the expansion tank was on the hot water side of the water heater. It had been there at one time but was moved to the cold water side about 5 years ago. I had forgotten about that.

Thanks again for all the assistance in solving this problem.