Hot water in cold water pipe with Recirc pump

[wenw80]

Hi all,

problem:

for the last 6 months or so I have started to notice an issue in my plumbing where I would get hot water in the cold pipes. Most severe at the sink right above the water heater and in the kitchen (likely the end of the line).

setup:

I have recirc pump hooked up to the water heater with a dedicated return line. Recirc pump is pumping return water into the drain outlet on the bottom of the tank.

diagnosis and things I have tried:

I have changed out all the mix cartridges at single handle showers and shut off washer machine pipes when testing. Did not help.

I have noticed that the cold inlet of the water heater is hot. When the cold pipes get cleared (running cold water or warm water), the inlet pipe feels cool, as soon as the faucets and showers get shut off, within seconds the cold inlet pipes will get hot again. There is no check valve or overflow tank. The dedic

also noticed that when I turn off the cold water inlet to the water heater the cold pipes do not get nearly as hot.

e sink above the water heater gets the hottest, and even when it eventually cools down, I can feel pulses of warm in the stream.

noticed if I turn off the Recirc pump the cold pipes are much cooler.

I’m thinking hot water is getting pushed up the cold inlet pipe and into the cold water lines. May be caused by the increased pressure from the Recirc pump pumping hot water back into the water heater.

am I missing something? Any help would be amazing!

 

[Jeff Handy]

You might need new heat trap nipples on both hot and cold.

My first thought was crossover, but you seem to have addressed all the single handle valves, which are a common cause of that.

 

[wenw80]

I’m still not 100% sure it is not a crossover, the other test I ran is turning off the cold water inlet at the top of the water heater, turning off the Recirc pump, and draining the hot water pipe through a faucet. After the hot water drained, it should stop right? Mine does not, and cold water starts to come out of the hot faucet... doesn’t that imply cold is crossing over to hot somewhere in the system?

 

[SHEPLMBR]

what kind of recirc system do you have?

 

[wenw80]

Grundfos with a dedicated return line. (Not a comfort system)

 

[SHEPLMBR]

Have you checked the check valve?

 

[gmcmurry]

I have a Kohler shower valve that has two check valves inside that have to be changed every couple of years or I will start getting hot water in the toilet that is a few feet away.

Its not just the valve assy to check. The little check valves are often overlooked.

 

[HWSleuth]

You must have a operating check valve between heater and pump. If you currently have a check valve be sure it’s not scaled up and in an open position. Even though the pump is running, cold water from the bottom of the water heater will back flow from the heater without an operable check valve.

If you have a cutoff valve at the pump, turn it off. If this solves the problem, you need a check valve or replace an existing one. We see scaled up check valves regularly causing this problem.

 

[wenw80]

I do see a check valve between the heater and the pump, but the pump and return line is connected to the drain line of the heater at the bottom (see picture), also the return line pipe is always warm, probably because the pump is always running. So not sure if that’s the issue

 

[wenw80]

I have a Kohler shower valve that has two check valves inside that have to be changed every couple of years or I will start getting hot water in the toilet that is a few feet away.

Its not just the valve assy to check. The little check valves are often overlooked.

Yeah there’s a pressure balance valve inside that’s most likely the culprit because it has a diaphragm between cold and hot. Is there a reason to change the outside mixer? Doesn’t seem like anything would wear out to cause a mix there is there?

 

[Jeff Handy]

Kohler will send you both parts, likely for free.
So get both, and change both.
Ask for extra seals and o rings, they get damaged or lost sometimes during install.
They will send a little silicone grease.

Put the old mixer in a labeled ziplock in your junk drawer, to put back in when the new part goes bad someday.
To use while parts are being shipped to you.