Rinna Tankless Water Heater: Pressure Issues & Expansion Tank Leak

[MethodicalMind]

Background:
My house is a new build, currently two years old. Last year, I measured the PSI from the expansion tank without any issues. Recently, out of curiosity, I tried to get a PSI reading again but this time a small amount of a sticky, clear fluid (possibly sealant) slowly leaked from the valve.

Pressure Regulator Valve (PRV) Status
I haven't experienced any issues with the PRV discharging.

Previous Plumbing Issue & Pressure Readings
During the first year, while the house was still under warranty, a plumber came to investigate a low-pitched screeching sound coming from the shower head. He said it was due to low water pressure and subsequently increased the pressure using the PRV on the main line that's located in the garage. While he believed the issue was resolved, I remained somewhat unconvinced; i was still able to hear the pitched sound.

During his pressure testing we noticed a discrepancy in pressure readings: the pressure gauge on the main water line inside the garage read 100 PSI (static), while the hose bib at the front of the house read 80 PSI. The plumber did not explain this difference, nor why he relied on the hose bib reading for adjustment. Needless to say he adjusted the hose bib to 80 PSI and therefore the gauge on the main water line always read 100 PSI.

Possible Expansion Tank Issue & Closed System
My home likely has a closed water system due to the presence of a backflow preventer valve associated with the in-house sprinkler and irrigation systems. This is likely why the expansion tank was installed with the tankless water heater.

Questions Implied

• Is the leaking fluid from the Schrader valve a definite sign that the expansion tank has failed? If so, why might have that happened within 2 years?
• Why the 20 PSI discrepancy in static pressure between the gauge on the main water line and the hose bib?
  • How do i know which pressure setting to trust?

Link of the high pitched sound of the shower head:

 

[CT-18]

Is the 100 PSI reading before the PRV in the garage. You should have consistent pressure on the house downstream of the PRV. You should only be getting air or water at the Schrader valve unless maybe something is breaking down inside the expansion tank. Testing at a hose bibb is a good spot to screw on the gauge unless you have a older style laundry tub faucet.

 

[GReynolds929]

Regarding the showerhead squeal, if it is a tub/shower faucet and the tub spout has a diverter that you pull to turn on the shower, the squealing is usually the tub spout washer not fully sealing. Replace the spout and see if the squeal persists.

Pressure gauge can vary in their accuracy and go bad regularly. I would check pressure at the water heater cold service valve with a new hose bib gauge and see what it says. If it is different from the house valve I would replace the house valve.

On a good thermal expansion tank properly precharged, you should only get air when depressing the Schrader valve. I would suspect that yours is failing. The tank should be precharged with air to the house pressure. If that didn't happen when pressure was increased that can lead to premature failure.

The galvanized pipe on the tankless water heater is not a good idea. It will release bits of rust and corrosion that will at minimum clog the inlet filter. Any galvanized piping should be replaced with brass, copper, or PEX.

Tankless water heaters need to be descaled and flushed annually at minimum. If this has not been done it should be done soon.

Most residential reducing valves have a max pressure of 75-80 psi, yours should have a tag stating what it's max regulated pressure is. If your pressure is higher than that the valve has failed. Also to note it looks like you have fire sprinklers, that usually means they want a minimum of 70 psi to ensure adequate flow from the heads. Code max pressure is 80 psi in a residential dwelling.