Needing expansion tank after changing waterheater?

[bigbird454]

Long story short. Recently had old water heater, 40 gallon Bradford White, replaced by a new plumber with an American Standard. (New plumber was at the house working on a remodel so we used him instead of calling our tried and true plumbing co.) Now we have water coming out of the pressure relief valve whenever we use a lot of hot water (washing 3 loads of clothes). New plumber either does not care or does not seem to believe this. After educating myself, looking at the American Standard owners manual, I believe we need an expansion tank. We are on a closed system, with a pressure relief valve on cold water line. We have also lowered the thermostat on the water heater, lowest position. Why didn't we have this problem with the Bradford White water heater? Is there something special about them? Do they have special features other water heaters don't have? Many thanks.

 

[Reach4]

You possibly need a larger expansion tank. The new HW tank may be larger, or may be set hotter.

You may have used more HW having built up a backlog of laundry and showers. The old one may have only had half of its hot water replaced with cold each time, but the new one had almost all of its water replaced with cold, as you worked down the backlog.

The precharge would ideally be set to the maximum water pressure the city supplies (4 am typically). But setting it a couple psi higher than the daytime water pressure is good. The air precharge should be set with the water pressure near zero. Of course getting a new WH did not change the water pressure from the city.

It is also possible that the existing expansion tank happened to fail -- just coincidence.

 

[Sponsor]

 

[Phog]

A dripping faucet, running toilet etc can also serve to relieve the pressure from hot water expansion, if you had any existing fixtures updated & the old leaks are now gone, that could be why.

 

[Terry]

If you pick up a pressure gauge you can check the static water pressure in the home.
PSI over 80 gets a pressure reducing valve. They can fail over time.

 

[WorthFlorida]

The old water heater the pressure relief valve could have had corrosion at the valve and prevented it from opening.
As said before the cause of your current problem is the cold water is expanding enough that the pressure is getting somewhere around 150 psi or close to it. As Terry suggest, get the pressure gauge with a tattletale needle. The pressure needle will push the red needle to the highest pressure and it will stay there until you manual move it back to zero. This is so you don’t have to babysit it.