David Starr wrote:
I've got a 4 year old 40 gallon gas water heater. Every now & then,
the T&P valve opens and 3 or 4 gallons drain out. The temp isn't set
too high - 1 on a 1-3 scale - so I don't think it's getting too hot.
It seems to happen when I'm using a fair amount of hot water for a
long period of time.. I have a home darkroom & sometimes need water
at 75 degrees for a couple hours; this is when I notice it happening.

Would it be a good idea to replace the T&P valve, or what? Do these
valves deteriorate over time? The valve appears to be doing what it's
supposed to, but I can't figure out why it's happening. Our previous
water heater never did this.

The T & P will open for either of 2 reasons:
Hi Temp
Hi Pressure

Unless the water is scalding (you say it's not),
very likely hi pressure is to blame.
And that is often due to "thermal expansion"
which occurs when the water is heated.

Good info he
http://www.stateind.com/expansion/expansion.htm

Or...do an Advanced Search he
http://groups.google.com/
It's been discussed on this ng many times.


Jim