Combi shutoff & therm expansion rlf options

[molsoncanadian]

Hello folks, I have a home with a gas water heater system. About 6 years ago, I had this same valve replaced and now I recently heard a hiss at the heater and discovered continuous water emitting from this valve yet again.
This time I want to try n replace it myself since I now know it’ll have to be done again in 5-7 years when it leaks. My line pressure after the PRV is ~50psi.
I’ve done soldering but never played with PEX. So I got a few Q’s for you Pro’s....
1- is the one I have considered a sweat x sweat x PEX unit?
2- why do these develop a leak? (Can it be related to a recent shutoff to replace a shower cartridge?)
3- the one I have is set for 80psi. I’m having a hard time finding one that is not 125psi. Almost as if they don’t make 80psi no more. The PEX pipes in the home are rated for 100psi. Would getting a 120psi relief not defeat the whole purpose of protecting the piping in the first place?

 

[Breplum]

Consider going with a conventional thermal expansion tank off of a 3/4" tee on the cold water supply and then a conventional shut off.
Looks like c x c x ips (or PEX barb).
Not enough photos to give further elucidation.

 

[Sponsor]

 

[molsoncanadian]

I am going to shy away from an expansion tank as space is quite limited, although it probably would've been a more permanent solution.

Is going with a 120psi relief going to be a problem with the piping in the rest of the home? (The pipes have a max psi of 100psi printed on them)

 

[Bannerman]

Water cannot be compressed. When cold water water is heated in the WH, the water will expand, but as the PRV will prevent the expansion from flowing back into the municipal water main, the house plumbing pressure will then rapidly rise significantly higher than the usual 50 psi regulated pressure. Without a thermal expansion tank to limit the pressure rise by absorbing the additional water volume, then something has to give.

Most WH relief valves are rated to discharge at 150 psi. Even so, a T&P valve will often seep to relieve some of the additional pressure caused by thermal expansion. Although you said your current relief valve is rated for only 85 psi, it seems it wasn't reliving the pressure from thermal expansion, instead resulting in pressure stress to the entire plumbing system, causung the weakest component to fail. While you are anticipating the same valve will fail again in 5-7 years, it could be another component that fails within a week/month/year, which could result in substantial water damage to your home.

Without an appropriate alternate method to allow for thermal expansion, an expansion tank is not an option but is essential.

 

[Reach4]

2- why do these develop a leak? (Can it be related to a recent shutoff to replace a shower cartridge?)
3- the one I have is set for 80psi. I’m having a hard time finding one that is not 125psi. Almost as if they don’t make 80psi no more. The PEX pipes in the home are rated for 100psi. Would getting a 120psi relief not defeat the whole purpose of protecting the piping in the first place?

A. The water heater itself will have a 150 psi relief, which may dump water onto the floor.
B. That pressure relief is probably there to keep the 15o from being ever reached. It may be instead of a thermal expansion tank.
C. I don't know why that PEX is marked 100 psi.
D. 75, 80 and 100 psi pressure relief valves are very common in well work. Many are adjustable, and many are fixed. They are often put in in case the pressure switch fails.

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https://store.dukesbuildingsupplies.ca/product-p/2308088.htm

 

[Dana]

I am going to shy away from an expansion tank as space is quite limited, although it probably would've been a more permanent solution.

An expansion tank on the water system on homes with pressure reduction valves or check valves preventing back flows from the house into the public water system is required by code in most of the US. On homes fitted with those valves a vacuum breaker might be needed too. Not sure if that's the case in Ontario. Not sure if you have a check valve or pressure reduction valve on your potable water either.

What is the static water pressure (at zero flow) in your house? In a home with 50 psi static pressure it's easy to exceed 150psi pressure spikes from "water hammer" whenever flow is interrupted quickly, like the solenoid actuated fill valves on clothes washers, or even when turning of a shower mixer. The longer the run and higher the flow, the greater the water hammer effect. (Do you hear the pipes shake & bang when the water turns off?) Installing water hammer arrestors near appliances or taps can reduce the peak pressures by quite a bit. If the pressure relief valve is chronically getting tripped open with small burps from water hammering grit can catch in the valve seats causing it to seep. It can also just plain wear out the valve seat.

Is going with a 120psi relief going to be a problem with the piping in the rest of the home? (The pipes have a max psi of 100psi printed on them)

Do you really have to ask?

If the static pressures are a large fraction of the 100psi max rating of the pipe and the PIPE has to absorb the water hammering or overpressures from water heating you're letting the pipe become the expansion tank, not exactly what it was designed for.

 

[molsoncanadian]

Thanks for all the support guys! The water hammer subject has got me sleeping a lot less lol.
I do hear the pipes moving within the walls when someone opens n closes the water.
Gonna get a pro to come in and make a decision for me. Its getting complicated. Last thing I need is a plastic pipe to blowout before the "next" relief valve wears out