bad pressure balance cartridge?

My sisters new home addition has an issue with the new shower. After a few months of use the shower now has low hot water pressure. the cold pressure is fine, and the hot pressure everywhere else in the old and new portions of the house are fine.

Info:

-As you turn on the shower (i.e. Cold water only) the pressure is fine. It drops as you rotate the valve mixing in the hot water.

-Old house and new addition share one hot water heater.

-New addition plumbed with 3/4" PEX.

-Valve is a MOEN PosiTemp model.

-Home has hard water (no softener yet) which I have heard can effect pressure balance valves.

My only idea is that it could be a bad pressure balance cartridge. It seems unlikely though after only a few months even with the hard water. I would think it would either be bad out of the box or bad after a few years, but a few months is an odd time interval. I also would think that if the plumber didnt flush the lines fully that the gunk would have caused the problem immediately after installation.

Any ideas?

Note: I know this is probably covered under the home warranty - I just like to know what the probem is ahead of time so I can be informed.

Call 1-800-BUY-Moen and get a free cartridge.

It is debatable what home warrantees do cover...

Usually less than the home owner expects....

Sounds more like there's some crud caught in the hot supply line, maybe an input screen.

You could shut the water off, take the cartridge out, turn it on momentarily to both flush the lines and see if the flow is good...you'll only need a couple of seconds. If the flow is good, it's not the cartridge. On a new one, it should come out fairly easily.

water

You said this was a new addition, so it should be covered by the plumber's warranty. YOU do not have to know anything about it. Just tell him the problem and let him solve it.

problem solved

well it appears that I solved the problem. I took the trim off and immediately noticed that the HOT valve stop was not turned on (the valve was at about 45degrees, only half on). There was still good tension on the valve so I don't know how it could have moved by itself. I am assuming it moved (from the fully open position) since installation because my sister and her husband said the hot pressure was fine for the first few months, and that this issue just came up. I am still puzzled as to how the valve got partialy closed - but hopefully it stays open now.

PS - The rough in valve is a MOEN Model S932. Anyone else experience this problem with this valve?

The installation instructions talk about setting the hot limit. Someone may have mistakenly adjusted the volume control verses the mechanical limit stop which prevents the valve handle from supplying too much hot. They are not the same, and to work properly, the supply stops should always be fully open.

As I originally thought...there was an obstruction in the supply.

jadnashua said:

As I originally thought...there was an obstruction in the supply.

Click to expand...

LOL, yeah I did too - but I was thinking more like gunk from the lines not being flushed - not a partially closed off rough in valve. That is not a mistake a licensed plumber should be making.

As it turns out - I asked my sister and she said she saw the apprentice doing the shower installation. Clearly the master plumber never checked his work. I just hope that guy made good PEX connections. They are all the Wirsbo type joint....hopefully good ones.