Shower temperature issue

[drew53813]

I am wondering what could cause the water pressure to drop and water to turn cold when other fixtures i.e. washing machine running, flushing a toilet are being used in our master shower. To give a little background my house was constructed in the mid 1960's. The shower is over 25 years old with an american standard single shower handle. I have copper t/o the house, 3/4 branch lines with 1/2 lines going to the fixtures. When nothing is being used the temperature is consistent and never drops pressure. My water heater and main line are in the garage and the approx run from the water heater to the shower is about 20-30 feet. I am thinking of replacing the shower valve cartridge but want to make sure I'm not missing anything obvious. Thanks- Andrew

 

[WorthFlorida]

How long have you had this problem?
New shower valve bodies have a pressure-balancing valves such as the Moen Posi-Temp models. When the water pressure drops on one side, the valve moves to close off one side of the water flow. As in your case a cold water valve is opened, the cold side drops in pressure, therefore the posi-temp feature will close off the hot side so as not to get temp shock.

https://www.hunker.com/13415447/what-is-a-posi-temp-faucet

 

[Sponsor]

 

[Jadnashua]

It sounds like you may not have an antiscald valve, or if you do, the spool valve is sticking some. If you do have one and it's working properly, the temperature would stay about the same, but the total volume would drop. On a shower, that would also appear to be lower pressure out of the head, similar to what you'd see on a hose sprayer if you started to turn off the valve.

 

[Terry]

The easiest and quickest fix may be to add an expansion tank to the water heater. A standard tank for that would be 2.2 gallons and that will help to buffer the ups and downs of the pressure in the system.

The next step would be to change out the valve to something pressure balanced. The A/S from the 60's won't do that for you. It's old school and no longer even allowed to be installed.