Cold water back up into hot water pipe

[lach_v]

Hi.
I have a problem: Cold water back up into hot water pipe. I think there might be something wrong with a shower valve since water out of a shower comes out barely warm. And even when the shower is off the cold water goes back into hot water pipe and again barely warm water comes out of hot water facet in nearby sink.
Question: any ideas why is this happening and how to deal with it?
The shower maker is unknown/could not find it, but it looks 5-6 years old (definitely not older) and it's a single handle shower with no tab.
Thank you.

 

[Jimbo]

If there is a crossover connection between hot and cold, then yes cold water will back up into the hot pipe. However, once you run the faucet or shower, you should get hot water.

The crossover can be a defective shower cartridge, or could even be in the sink faucet.

 

[Sponsor]

 

[lach_v]

Thnaks for quick reply! There are 2 showers and a sink sitting on the same set of pipes. Sink can be eliminated - I cut the water under it and it didn't help. I already cut the drivewall and by just feeling the pipes tempreture can tell this.
So it must be one of 2 shower cartridges...
Is there any specific way I can tell which one is defective?

 

[Jimbo]

What brand are they? Moen can have this happen. Mixet is notorious. And in the case of Mixet, replacing the cartridge does not fix the problem. There is wear inside the body. There is a cartridge for about $100 called NOmix which fixes it.

 

[lach_v]

I am not 100% sure what brands are they. Looks to me that 1 is Kohler (K-304), another - Price Pfister (shown here http://www.**************.com/pdf/0X8-340A-3.pdf). But neither one looks even close to Why can't they put a brand name somewhere visible???
I'll try to post pictures tomorrow.
Thanks again!

 

[lach_v]

Here are the pictures. As I said first looks like Kohler, another - Price Pfister:
http://picasaweb.google.com/lachinov/Plumbing#

 

[Jimbo]

2 is definitely PP. 1 does look like Kohler. Neither of these has a "history" of x-over problems, although anything is possible.

Do you ever leave a valve turned on, using a small stop at the shower head to keep the water off? That leads to thoughts about the washing machine. Try turning off both taps to the WM and see if symptoms change. Do you have a tempering valve anywhere in the house??

 

[lach_v]

We rearly use those showers at all - since they are in the basement. But when we use them - we turm them off by valve.
WM was also my first thought - so I eliminated it long time ago by trurning off water supply to it.
And as far as I know I don't have tempering valve - but, oboisly, I didn't build the house. I'll call PP and order a new balancing cartridge.
Thanks!