Hot water in cold pipes (Recirc pump with dedicated return line)

[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!

 

[Breplum]

There should always be a check valve at the return.
One thing to try: Shut off cold supply to WH. Turn pump off and check a hot water tap for flow after everything depressurizes.
Does all water flow stop? If so, there is no crossover. If it doesn't stop flowing then there is crossover.

 

[Sponsor]

 

[wenw80]

There does seem to be a check valve at the return between the pump and the water heater. Attached are a couple of pics.

I have turned off the cold water inlet to the WH, hot side flow has been decreasing, though after a few minutes it’s still flowing, at first warm water, now the flow is cold water. Seems like I still have a cross over?

besides shower cartridges where else could there be a cross over?

 

[WorthFlorida]

See if you have a check valve at the cold water inlet. In your our setup the recirculator goes to the bottom of the WH and it appears there is a check valve at the return line after the recirculator. This check valve prevents water from being drawn from the bottom of the tank (cold or cool water) when the circulator is off and you are drawing water at a fixture. The check valve at the top of the water heater in this picture prevent hot water from being drawn from the tank and the recirculation pipe when cold water is be used. The check valve at the bottom of your unit can be opened for inspection.

Check valves get jammed open from minerals or spring loaded type the spring breaks. Most water heaters have a heat trap right at the cold water inlet that acts like a check valve. They are installed at the factory for residential WH. There is a ball inside these couplers and they can wear out and fall into the tank. https://www.bradfordwhite.com/heat-traps-bulletin/

 

[WorthFlorida]

 

[wenw80]

Thanks for the info!

Are there good ways to test if either of the check valves? (1. the one on the return line at the bottom, 2. cold water inlet heat trap)?

 

[wenw80]

Also, some have suggested that a recirculation system typically do not have heat traps at the cold inlet, is this true? What's the reasoning behind that?

 

[WorthFlorida]

Also, some have suggested that a recirculation system typically do not have heat traps at the cold inlet, is this true? What's the reasoning behind that?

I doubt that statement. Get the name brand off of your circulator pump and look up the installation instructions. The manufacture should have a few different ways on the install depending on a few variables.

 

[wenw80]

Thanks, is there a way to determine if it’s the cold water heat trap that’s faulty or a crossover? If there’s a crossover, would the cold intake pipe still get hot? Or does that only indicate a heat trap issue where hot water from the heater is being pushed up the cold water inlet?

 

[Jeff H Young]

looks like Grundfos pump , why not throw a check valve on the cold water feed to w/h? (I think you would need a expansion tank if you do that) . I hear a bad pressure balance spool at shower valve can cause mixing of hot and cold water . maybe pull cover plate off your shower valve and put your finger on the hot and cold pipes feeling the temp if they're both hot I'd suspect the pressure balance spool.
Breplum idea is quicker and easier than the above ,

 

[wenw80]

looks like Grundfos pump , why not throw a check valve on the cold water feed to w/h? (I think you would need a expansion tank if you do that) . I hear a bad pressure balance spool at shower valve can cause mixing of hot and cold water . maybe pull cover plate off your shower valve and put your finger on the hot and cold pipes feeling the temp if they're both hot I'd suspect the pressure balance spool.
Breplum idea is quicker and easier than the above ,

Breplum’s test is the only reason I still think it could be a cross over, because shutting off the cold inlet to WH, cold water comes out of the hot faucets after a while... anyone have any good ideas on how to eliminate possible cross over points? (Showers with no shutoff valves)

 

[Jeff H Young]

yes I got ideas but first clarify . You said hot water comes out the cold at kitchen and another sink Correct? Then with cold water feed to w/h closed check every bathroom . But it sounds like the one above kitchen pull plate like I said and feel those pipes if they are both hot that's the bad one

 

[wenw80]

The sinks all have non-mix faucets, so I don’t think those are issue, the issue is the showers, and the problem is the pipes are not exposed for me to feel them. Is there a way to plug up the holes in the valve to eliminate the possibility of a crossover at these showers? I have replaced the pressure balance valves on these, but can’t be sure it’s still not mixing... best is if I could bypass these to narrow down to the problem... any ideas?

 

[Jeff H Young]

the lavs have nothing to do with it as you said and don't want to imply its a lav issue .
Its your shower valve . I cant tell you which one it is how could I know? your shower valve might have stops but you cant get to those either right ? in which case change the balance spool on one and if it doesn't change go to next and so on till problem goes away pretty simple . but Id start at the room that got hot coming out the lav

 

[Jeff H Young]

took another look why cant you bust out some of that excess tile around the cover and tell if its warm or has shut off valves

 

[WorthFlorida]

A dedicated return line system has no crossover check valves. With a non dedicated return line where the cold water line is used is when a crossover is needed and it is a common point for failure.

To test, at all sinks close the shut off valves both hot and cold including the washing machine valves. At the showers close off the stops (if there are any). With everything thing closed off at the sink that is the worse, open the cold water valve and run the cold water. If it gets warm or hot the problem is at the WH. My first suspicion is the check valve right after the pump. It easy enough to open and check it. If it looks good look at the cold water pipe if there is another check valve. If not and during the test the cold inlet pipe is warm, then the heat trap is suspected.

Another thing is if there is a shut off on the return line before or after the pump, close that valve and turn off the power to the pump so you are not using the recirculating system.

There is no single or simple answer to where the problem is. My entire working life was troubleshooting and testing communication systems. As always, eliminate items then isolate the area in trouble. You did good by replacing the shower valves as something I would have done. It's easy and eliminated a mixing possibility. At one time washing machines could caused a mixing problem. Something my father found out in the early 60's with an old machine.

 

[Jeff H Young]

never heard of washing machine mixing water or if that's possible with todays (his) machine but same investigation grab the bibs if they both hot its possible close the valves if it persists forget that possibility in this case. I'm about 95 percent sure its at shower valve. good luck! let us know how the diagnosis and repair go.

 

[Reach4]

You don't have one of these hooked up somewhere, do you?

 

[WorthFlorida]

never heard of washing machine mixing water or if thats possible with todays (his) machine but same investigation grab the bibs if they both hot its possible close the valves if it persists forget that possibility in this case. Im about 95 percent sure its at shower valve. good luck! let us know how the diagnosis and repair go.

That was a lot if years ago. A Westinghouse semi front loader. With four kids in the house it was well used. It looked just like this.https://www.worthpoint.com/worthopedia/vintage-washing-machine-mcm-1930522022

I wonder if the kitchen faucets that are touch or motion control could be a source of cross over. The one my son has you need to keep the faucet valve opened in any position. Works real well and you sure can get used to it.

 

[Jeff H Young]

I put foot pedals in my brothers kitchen when remodeling.
I'm thinking shower valve but ?