Home>Discussions>PLUMBING>New Expansion Tank/T&P Valve Still Leaking
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mpriley05
New Expansion Tank/T&P Valve Still Leaking

Our T&P valve has been leaking for months. We would just turn the cold water off to the water heater to get it to stop. We finally had our landlord install an expansion tank. It's installed, but the T&P valve still leaks continuously. The pressure coming into the house is 40 psi. I checked the pressure on the tank - it's also 40 psi. The expansion tank fills up as the water heats and expands, and when it's full, the T&P valve leaks until we use some hot water or turn off the cold water to the heater. Any thoughts?

JLMCDANIEL
Re: New Expansion Tank/T&P Valve Still Leaking

Bad T&P valve or dirt in the valve. Try opening and closing it a couple of times to see if it flushes out dirt, if not replace valve.
Jack

mpriley05
Re: New Expansion Tank/T&P Valve Still Leaking

I forgot to say that this is the second valve for the water heater - I tried that before anything else. It's been flushed several times over the past few days. Should I get a new valve? Could it be anything else?

goldhiller
Re: New Expansion Tank/T&P Valve Still Leaking

When you say that the tank pressure is also 40psi...do you mean you checked the air pre-charge and it was 40 psi?

Have you tried depressing the air fill valve on the expansion tank when the T&P is leaking? If water comes out then it means that the internal bladder is faulty/has a tear in it... and there is no air cushion. Just a quick tap on it should tell you. The longer you hold it down, the more air pre-charge you will lose if it still has a pre-charge in it.

The problem may prove to be in the T&P though, as Jack suggested.

Am also curious as to when/why this problem first began. Was something changed and then the problem suddenly appeared? City installed back-flow preventers on the water lines, maybe?

JLMCDANIEL
Re: New Expansion Tank/T&P Valve Still Leaking

40 psi should be absolutely no problem, I beleive the specs for a T&P valve is to release between 124 and 150 psi and 210 degrees F.
Jack

canuk
Re: New Expansion Tank/T&P Valve Still Leaking

or the temperature is set too high on the tank and the T&P is doing it's job.

goldhiller
Re: New Expansion Tank/T&P Valve Still Leaking

Or the expansion tank is too small for the size of the water heater

Or there is a faulty thermostat failing to shut off the current to the heating element or gas burner when it should

goldhiller
Re: New Expansion Tank/T&P Valve Still Leaking
JLMCDANIEL wrote:

40 psi should be absolutely no problem, I beleive the specs for a T&P valve is to release between 124 and 150 psi and 210 degrees F.
Jack

Understood. What I'm wondering is when was the pressure checked. Maybe the tank had no precharge at all. Ya never know.

mpriley05
Re: New Expansion Tank/T&P Valve Still Leaking

Precharge was checked before installation the first time, and then again yesterday after I disassembled the installation specifically so I could recheck the pressure.

No water comes out of air valve, although the expansion tank is full of water.

The water heater is 40 gallons, the expansion tank is 2 gallons. According to package, this tank is the right size for the water heater.

The temperature is set to 115 F. The T&P label says it pops at 210 F and 150 psi.

The landlord said they have had a history of this problem.

Right now, the cold water to the water heater is off. I'll turn it back on and check the house pressure when the T&P starts leaking.

Goldhiller may be right in that the thermostat in the heater is bad. This T&P leak is nonstop when the breaker to the water heater is on and the cold water supply is open to the water heater. it seems like it's a never ending cycle - the water heats and expands, forcing some out the T&P, then new cold water is supplied to keep the tank full, and this expands, which is forced out, requiring more cold water, etc. etc.

Do any of these answers change any of your diagnoses? Thanks for the replies.

goldhiller
Re: New Expansion Tank/T&P Valve Still Leaking

Where is the expansion tank installed?

If on the incoming cold water line and the WH has a built-in/integral check valve in that incoming line....no "expanding" water can get back to the expansion tank. This would render its prescence...moot.

The landlord said *they* have had a history of this problem

You lost me. ;) What has a history of this problem?

(Will take a wild guess. He's saying that these particular WHs have had a hsitory of this problem when they install them to replace existing WHS. If so, me thinks that the houses in question probably have PRVs (pressure reducing valves) that allow backflow into the city supply. The old heaters had no check valves to prevent backflow from expansion reaching the PRV to relieve itself, but the new WHs do and so a problem commences upon installation.)

Blake
Re: New Expansion Tank/T&P Valve Still Leaking

Does this water heater have heat traps installed that may be checking the expansion at the water heater?

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