Hot water coming out of upstairs cold water side

[dudrick]

Hi,
Will someone please tell me if it's true that I need a check valve in the cold water supply to my DHW tank to keep hot water from migrating to these 2nd story bathrooms? Thanks.

[havasu]

Although some municipalities require a check valve to prevent the flow of water from the house back to the water main, generally it is not necessary. If you do decide to install one, make sure you install an expansion tank in between the valve and the water heater. If you don't, you will run the risk of having a water leak from your pressure relief valve when the water heats up and has no place to go due to the check valve.

[phishfood]

I think that the poster is asking a different question than you are answering, havasu.

If I understand correctly, the question that is being asked is this. Is the hot water from the downstairs water heater making it's way into the cold water supply lines that are serving the upstairs fixtures?

My answer would be that there are certain piping arrangments that can allow this to happen, though it is rather complicated to explain.

So if the original poster is actually experiencing a problem with this, I would say that a check valve on the inlet supply to the water heater would either fix the problem or rule that out as the source of the problem, at a relatively inexpensive price point.

[dudrick]

I put the check valve on and also cleaned the balancing valve on the single handle tub/shower faucet.
No more migration but the hot water side is now not getting as hot as before.
Did I do something wrong with the balancing valve or does it need to be replaced?

[phishfood]

Often times, there is an adjustment on the tub/shower valve that allows you to set an upper limit for the amount of hot water that can be allowed into the valve. Usually this is accomplished by means of what looks like "gear teeth" on the handle assembly. If you remember something like this on your valve, you can very likely take the handle back off and adjust it to allow more hot water into the valve.