Water heater expansion tank

[laa_guitar]

I just installed a new electric water heater and the T&P relief valve (150 PSI) has "popped" open several times. At the time I had the water temperature set to ~130 degrees F. Since lowered to ~120 F and not "popping" any more. I decided I needed an expansion tank after doing some reading. When I went to install the expansion tank, the instructions said to put a pressure relief valve of 100 PSI or less on the line or the warranty would be void and that pressures in excess of 150 PSI could cause the expansion tank to burst. The tank was tested to 120 PSI and rated at 150 PSI maximum. The T&P valve on the water heater is 150 PSI and it has "popped" as explained above.

1. If I install the expansion tank and replace the water heater relief valve (150 to 100) won't it be that much worse than it already is?

2. Or, should I leave the 150 PSI valve on the water heater and add another one (100 PSI) with the expansion tank?

3. If I do (2) above, is the addition of the expansion tank really going to absorb the difference in pressure of 150-100=50 PSI? or will the 100 PSI relief valve begin to "pop"?

4. When the water heater relief valve "pops" at 150 PSI is the pressure on all of the plumbing lines also 150 PSI just prior to the "pop" and can the lines take that much pressure (up and down) for very long before they eventually start to leak? (PVC pipe up to the house and copper pipes in the house)

[Wgoodrich]

P29903.3 and P2903.3.1 dictates that the minimum water pressure of a dwelling plumbing system to be minimum of 40 psi and maximum of 80 psi. When the pressure exceeds 80 psi an approved pressure reducing vlave shall be installed on the water service pipe to retain within the maximum of 80 psi pressure.

Thermal expansion controll is required to be installed when the building supply pressure is greater than the relief valve setting.

You are stating pressure relief beyond the limits allowed for this water system.

Pressure relief valves shall be sized at least 25 psi higher than the system pressure mentioned above concerning minimum and maximum pressure.

Now I am suspecting that you are tripping due to temp rather than pressure.

Most water heater relief valves are both temp and pressure rated as a combined sensing unit. This relief valve is required to be installed in the top 6" of your water heater.

P2803.3 Maximum temp setting for a water heater is 210 degrees F or 99 degrees C.

If it were me I would replace that relief valve with a new one and ensure it was installed in the top 6" of the water heater tank.

Doubt you need the expansion tank. Your stats as stated do not seem to be out of line and the relief valve should not be popping.

Before you install this expansion system try replacing your pressure relief valve. Suspect you have a faulty relief valve.

Just my opinion.

Wg