Water Heater Expansion Tank


Premium Member
Sep 10, 2013
North Carolina
Hi all,

We have a new 50 gallon gas water heater, and the plumber installed an expansion tank with it. I don't know much about these expansion tanks, but ever since it was installed, the hot water feeding into the washing machine is under higher pressure than it used to be. Mind you, after about 10 to 20 seconds or so, the incoming pressure drops to normal levels when filling the washer with warm water.

This added pressure concerns me, and I am afraid hot water rubber intake hose could rupture.

Something doesn't seem right here.
You'll need to get the plumber to come back out to see what's going on, something doesn't seem right either.


The plumber said (during installation) the expansion tank was required by code now. The water heater is a Rheem 50 gallon professional series model, and I am assuming there is a check valve installed to keep back pressure off the intake line?

We do have good water pressure here, but I don't have a line gauge to test it with.

Are expansion tanks supposed to be filled with enough air to match the water pressure?
From what I've been told: Its purpose is to deal with thermal expansion of water as it heats up in the water heater - to prevent water pressure from getting too high, they are not code here in Arizona.

This is a more a plumbing question, and I'm not a plumber.:)

You should have a warranty on the work he did, did you have him come back out?

The city came out and did some pressure tests this week...

Static Flow - 110 PSI
2 Gallon Flow - 110 PSI
10 Gallon Flow - 80 PSI
Residual Wide Open Flow - 38 to 40 PSI

I am not quite sure what all of these numbers mean yet, but I have been given a phone number to call for further advice.

Do you know how much pressure a washing machine intake valve can safely handle? I read where too much pressure can shorten the life of said valve.
This is what your house is getting for water pressure--->Residual Wide Open Flow - 38 to 40 PSI

Which is perfect.

Do you know how much pressure a washing machine intake valve can safely handle?
80 PSI and under.

Yours are fine.

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