Plumbing – New plumbing – Lose Water Pressure in Outdoor Hose

A few things to check;

• Did you place the expansion tank on the cold water side?

• Did you pressurize the expansion tank to the same pressure that the water line is at after the regulator?

• Is the expansion tank size rated for the size of your hot water heater?

I think you have two completely separate issues that you became aware of at the same time, and which are mostly unrelated.

Improperly set system and air pressures in bladder tanks.

A note - the higher the system pressure, the less water storage (drawdown) in a bladder tank. So you might get better performance from a 40/60 or 30/50 setting.

You are also at risk of damaging the bladders by underfilling the air for the pressure you have set on the water side. The bladder becomes much more distended than it's designed to be, and lots of water simply sits in the tank with the effective volume of the tank greatly reduced, since the first water to enter the tank is raising its air pressure from your too low setting to where the pressure switch is set, and shrinking the air bubble to do that.

Low pressure on the second floor bathrooms is probably from a blockage.

Pressure due to elevation is 2.3 feet per PSI, so pressure on the second floor due to elevation is probably not really the issue (might be 8-10 PSI less than the basement in a typical house) and of course it worked fine until you drained the system; so it's not "really" pressure loss, in the sense of the pressure in the pipes - IMPE it is often the case that when you drain and refill a water system "crud" (usually harmless, but unappealing, deposits from the water) in the pipes gets knocked loose with all the bubbles passing through and will plug shower heads and aerators - that does cause pressure loss OUT of the showers and sinks. Try removing shower heads and aerators, cleaning them, and blowing the pipes clear without having them in place.

I would suggest draining the system again, verifying that the air pressure is still 38 (if not you may have a leaky bladder) and resetting the pressure switch to 40/60 (with a typical pressure switch, be sure to turn the pump breaker off before adjusting.) Then remove all showerheads and aerators, repressurize the system, and blow the pipes clear before reinstalling the cleaned showerheads and aerators.