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Hot water heater pressure relief valve

16 years ago

I'm swapping my old water heater that went out with one my friend had that is only a few years old. His had a top mounted pressure relief valve that has been removed and mine is a side mounted version. Can I get mine to work on his or should I just buy a new one for the top mount...and how much do they cost, or should I just not mess with a used heater and just go and buy a new one. I was trying to save a few bucks but it doesn't seem as simple as I had hoped

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Comments (3)

coolvt
16 years ago
i think the used tank is okay if it's not too old, but I would invest in a new pressure relief valve...less than $10.00. If the old one is plugged up it might not work and you could have a serious problem. Remember that to be safe and legal, the pipe coming off the relief valve has to run down to within I think it's 6" from floor level. This is so if it blows off water and someone is standing near by, they won't get it in the face. I would try to reuse any of the old piping that was attached to the old valves.
remodeler_matt
16 years ago
At the least I would take out the sacrificial anode from the one you want to install to see what kind of shape the inside of the heater is. If the anode is totally gone, covered in rust or calcium, I'd pass on it. A used water heater is seldom a bargain.
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You are getting closer to the 150 psi temporarily. That's really, really hard on all of your plumbing - especially the water heater. The P&T valve is the last line of defense against catastrophic tank failure. Do not allow that to continue. Install the expansion tank and set the pressure to 60 psi. If you want to up the size from the 2 gal to the 4 gal that's fine too. It will give you just a bit more cushion. Be sure that you support the tank - particularly the larger one - properly. Thanks to oneandonlybobjones for the sizing chart - I like it when people give references. weedmeister is correct about what the higher pressure does to things: It's hard on solenoid valves in washers, ice makers and dishwashers. It also exaggerates water hammer and stresses things like flex risers and flex hoses. Coming home to a burst washing machine hose that has been running for hours and having your furniture float out the front door when you open it is no fun. If you don't have enough flow at 60 psi you might look at cleaning aerators and such... but in general you shouldn't expect to pressure wash the dishes from the kitchen faucet.
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randy427
16 years ago
The following was posted by Lazypup on a similar question:

Both the ASTM (American Society of Testing & Materials) standards and the plumbing codes require that the sensing probe must be in the upper 6" of the water heater pressure vessel.
Typically they are side mounted on gas water heaters while they are commonly top mounted on electric water heaters. Either position is fine providing the T&P valve sensing probe is extending into the upper 6" of the internal pressure vessel.

Years ago water heaters did not have Temperature & Pressure Relief Valves. Instead they had "Pressure Blowout Plugs" which look like the freeze plugs in an automobile engine block.

When T&P valves first became available water heaters only had two threaded ports, hot & Cold, so they would install a close nipple and Tee on the Hot water discharge line and place the T&P on the top of the TEE with a long probe that extended through the TEE and nipple and into the upper part of the tank.

If your old water heater has a third threaded tap on the pressure vessl where the probe is extended directly into the water in the tank you may use a standard T&P valve. If the T&P is on top of a tee you must use an extended probe type valve.

If you need an extended reach type look for a Watts 100XL. The XL on the model number identifies it as an extended length probe.

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