Water Heater Pressure Relief Valve

[HeavyDuty]

I’ll pick up a gauge and check the pressure. I also assume I can then check the expansion tank with a tire pressure gauge, and adjust the pressure if needed? Is the expansion tank pressure read under load?

Beyond that, I might do better to call a plumber rather than risk really screwing things up.

[tadawson]

I’ll pick up a gauge and check the pressure. I also assume I can then check the expansion tank with a tire pressure gauge, and adjust the pressure if needed? Is the expansion tank pressure read under load?

Beyond that, I might do better to call a plumber rather than risk really screwing things up.

Relief valves are prone to issues, and in my 58 years, I have never had a home (or seen one) with a PX tank on hot water. Unlike a furnace, which is either a closed system, or has a pressure reg to fill only where thermal expansion needs a PX, a hot wather heater typicall does not have an inlet check valve, and as such, cannot build pressure beyond overall hot/cold water system pressure, since excess volume simply outflows from the tank back into the line. Unless it is horribly frozen, myself I'd just check the temp (the relief valves also have a thermal component, typically 210 degrees based on a quick search, in case of boiling) and if OK, change the valve - It's not rocket science or much more than $15 to $20 bucks . . If an older tank that can be set quite hot, you may not have much margin in the pressure/temp curve left . . .

Oh, and if you run your heater pretty hot, back the temp of 5 to 10 to test . . . costs you nothing, but can confirm a failing temp/pressure relief. (You don't mention, or I missed, how old this heater is . . .).

[HeavyDuty]

Hmm. I’ll check both the pressure rating of the current valve and the thermostat setting. It’s about 6 years old. When we were house shopping here in New England, every house with a water heater had a small expansion tank - it is probably code.

Do I use Teflon tape on the relief valve, or does it seal another way? Also, I’d still like to check the expansion tank pressure.

[tadawson]

Hmm. I’ll check both the pressure rating of the current valve and the thermostat setting. It’s about 6 years old. When we were house shopping here in New England, every house with a water heater had a small expansion tank - it is probably code.

Do I use Teflon tape on the relief valve, or does it seal another way? Also, I’d still like to check the expansion tank pressure.

Temp rated teflon tape would be my go-to. Most of the valves I have seen pressure release at 125 to 150, and temp at 210, but should be on the old one.

[hufnagel]

I went through all this not too long ago.
wound up replacing my pressure regulator and installing an expansion tank. now no more pressure spikes.
I will say, I had to reset my expansion tank after about a year. there was no signs of leakage, so maybe that's a thing that needs doing periodically?

[tadawson]

I went through all this not too long ago.
wound up replacing my pressure regulator and installing an expansion tank. now no more pressure spikes.
I will say, I had to reset my expansion tank after about a year. there was no signs of leakage, so maybe that's a thing that needs doing periodically?

If it's a bladder type tank, you should not need to do that (furnace on one of our properties is probably close to 30 years old - tank is still 100% and at correct pressure . . . never touched . . .).
If not bladder (or bladder failed) then you likely are having the "bubble" go into solution and losing it.

[NH Shooter]

Relief valves are prone to issues, and in my 58 years, I have never had a home (or seen one) with a PX tank on hot water. Unlike a furnace, which is either a closed system, or has a pressure reg to fill only where thermal expansion needs a PX, a hot wather heater typicall does not have an inlet check valve, and as such, cannot build pressure beyond overall hot/cold water system pressure, since excess volume simply outflows from the tank back into the line.

Unless you are on a public water supply with a pressure reducing valve, which has a check valve built in. If so then the excess pressure can NOT dissipate into the water main and an expansion tank is absolutely needed.

The gauge I linked to in my previous post will tell the story if there is an over-pressure situation due to thermal expansion. The typical temperature & pressure relief valve (150 psi, 210 degrees F.) used on storage water heaters will begin to drip at around 125 psi.

[HeavyDuty]

Unless you are on a public water supply with a pressure reducing valve, which has a check valve built in. If so then the excess pressure can NOT dissipate into the water main and an expansion tank is absolutely needed.

The gauge I linked to in my previous post will tell the story if there is an over-pressure situation due to thermal expansion. The typical temperature & pressure relief valve (150 psi, 210 degrees F.) used on storage water heaters will begin to drip at around 125 psi.

I ran over to Home Depot and picked up two sizes of pressure valve and some high temp pipe dope. They were out of the pressure gauge, though. The pressure at the tap doesn’t seem excessive, so I think I’ll try swapping out the valve first.

[HeavyDuty]

Pressure valve replaced.

The feed line shutoff valve doesn’t work (just spins,) so I had to shut off the whole house. Plus, the drain valve is plugged, the prior owner obviously never did yearly flushes. I’m planning on having a tankless heater installed, I’ll make sure they use ball valves.

I put a tire pressure gauge on the expansion tank and get nothing. I did find a backflow preventer on my side of the water meter.

What is a good starting pressure for the expansion tank? I’ll pick up a cheap bicycle pump.

[MistWolf]

Air pressure in tank should equal water pressure. Pressurize tank with zero water pressure in the lines.