Upstairs bathtub faucet won't stop leaking, at wit's end

[Caduceus]

If you went through three cartridges and a new valve already and it only happens periodically I would check for the thermal expansion issue effecting it since it probably needs to be addressed anyways. I have seen thermal expansion do similar things to shower valves, solenoids and toilets throughout the years after similar repeated repairs were made in homes. I could be wrong, but it's a start since the plumber seems to have given up.

 

[compddd]

Took off the old expansion tank, it was full to the brim with water and black crude. Installed the new expansion tank but the dripping and bursts of pressure from the faucet are still occurring. I was watching the faucet drip, and turned on the hot water in the sink next to the dripping faucet and the water came out at high pressure for 1-2 seconds and the faucet stopped dripping immediately. Just an observation.

Did I install the expansion tank wrong? My water heater is 50 Gallons and I got a 2.1 gallon expansion tank. I checked the water pressure of my house and it's 60, so I pre-charged the new expansion tank to 60 PSI before installing it.

Am I missing something here? Do I need a bigger thermal expansion tank? Did I pre-charge it too high?

 

[Caduceus]

If you could, please post some pictures of the water heater with expansion tank and your water service with meter and anything in line around the meter.
What you're describing sounds like the TET should have given you some relief from the issue and over-the-internet diagnostics can be tough. Maybe you have something else going on here in addition to the thermal expansion.
You can also still do the thermal expansion test to see if you are still getting increased pressure with the tank firing.

 

[KULTULZ]

Full of black crud, interesting.

The air charge in the TET should equal house pressure at ambient temp, i.e. without the water heater actually heating (cut power) and allowed to cool somewhat IMO.

Leave the test gauge on the laundry sink bib for 24hrs and see what you get.

 

[Caduceus]

Full of black crud, interesting.

The air charge in the TET should equal house pressure at ambient temp, i.e. without the water heater actually heating (cut power) and allowed to cool somewhat IMO.

Leave the test gauge on the laundry sink bib for 24hrs and see what you get.

Exactly, KULTULZ. "You will also need to know what the normal house pressure is so that you can pressurize the new thermal expansion tank to match it. Sometimes just by pressing the schrader valve and getting water instead of air out of it would be proof enough, but sometimes the schrader valve doesn't close back up and will keep spraying water until you get it shut off."
But 60 psi does sound like standard pressure. I'm just hoping that rechecking everything something wasn't missed. I've used the internet before for information and reread the advice, sometimes finding that I skipped a step or misread something when things don't go as planned.

 

[KULTULZ]

Full of black crud, interesting.

Let me clarify this a little...

This is similar to the also recent post of finding black particulates in the water as a result (supposedly) of the TET diaphragm being compromised by chlorine/chloramine or just simply a bad product.

Just to note also, the black particulates can also appear it seems as a result of any rubber washer deterioration in the system, say an angle valve or those fancy stainless steel braided hoses.