Posted by Will Harris, From: on December 30, 1999 at 06:27:21:

In Reply to: T&P Relief Valve releasing water intermittently posted by Elbridge Gerry Puckett on December 29, 1999 at 11:55:30:

You are probably in need of a thermal expansion tank. When water is heated, it expands. If you are not using any water, the pressure (due to the expansion) stops at your faucets and then backs up the cold water line until it runs into a check valve or PRV, which stops it. The pressure in your tank builds and the T&P starts to leak.

A thermal expansion tank is relatively cheap and will extend the life of your heater.

: I have a State Industries "Censible 510 E" 40 gal gas water heater which was manufactured and installed in 1990. The installation was in a new home in Davis, CA. The water is quite hard; I do not have a water softener. I replaced the anode on this heater in 1996 and the current anode is in reasonably good shape. The T&P Relief Valve on this heater has recently begun to release hot water, especially in the early morning (e.g., 6:00 am). The temperature of the water being released is approx 140 deg F. The T&P Relief Valve is more likely to release water when I increase the temperature of the gas heater, but over time it is releasing at lower temperatures.

: The tank appears to be in good condition. I replaced the hot and cold water nipples which
: had some small corrosion on the outside, probably due to a slightly loose coupling with the hot and cold lines. However, this did not stop the relief valve from engaging the following morning.

: One other possibly relevant piece of information is that I have a passive solar system upstream of the hot water heater. The
: system consists of an 40 gal Rheem (electric)
: water heater (the electrical heaters are not
: connected) with the cold water nipple connected to the water supply and the hot water outlet connected to my gas water heater. The drain of this electric water heater is connected to a heat exchanger through which is also flowing the solar heating fluid (methyl alcohol - I think).

: QUESTION: What are the likely causes of my problem?

: 1. Could it be a faulty T&P Relief Valve?

: a) Should I replace if first before
: trying anything else?

: 2. Could it be a faulty thermostat?

: a) But the water appears to be the
: correct temperature for the gas
: control setting I have selected.

: 3. A plumbing supply clerk told me it was
: releasing due to too much pressure in the
: line (i.e., not overheated water) and that
: possible causes might be

: a) A faulty check valve in a closed loop
: in the system,

: b) a pressure reduction valve, or

: c) new construction or recent work in
: the area by the water company.
:
: I don't believe I have a check valve in the system - except possibly in the heat exchange loop in the solar heat system.

: - I don't know if I have a pressure reducing valve.

: - There is A LOT of new construction in my
: area. But how could this cause the problem
: and what should I do to diagnose and solve
: the problem?

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