# Hot water on cold side of ks? Foam insulation.



## Texan (Feb 21, 2015)

Went on a call today where the ks cold side was warm to hot water for 10 to 30 seconds then gets cold and stays cold. Same thing at hose bib by ks and bathroom close to ks. 

The details
Tankless navian with recirc line.
Close isolation valves on wh problem stops.
Foam insulation in attic and ext walls.
No tempering valves in house.
No crossovers found.
The problem get worse the longer the recirc line runs with out running cold.
Big floor to ceiling Wine cooler by ks. House was just remodeled. All new copper plumbing that I cant see in attic(must be in the walls or slab). Except one insulated lone 3/4 copper line in attic, looks like a reroute. 
Kitchen is in ext wall 80' from wh.

My guess.
What I think is the recirc line is too close to the cold line heating it up cause its all cased in foam. Maybe behind that wine fridge. Told ho to get the top out guy out and ask where he ran the lines. His work looks ok from what I can tell but something is screwy. He's coming tomorrow to look. 
Long story for a simple question

Question.
Anyone had a prob with foam insulated recirc lines exchanging heat with cold.


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## rjbphd (Feb 5, 2010)

Texan said:


> Went on a call today where the ks cold side was warm to hot water for 10 to 30 seconds then gets cold and stays cold. Same thing at hose bib by ks and bathroom close to ks.
> 
> The details
> Tankless navian with recirc line.
> ...


What did you find out with the topout guy?? My guess that the lines will never freeze with this set up.. try unplugging the circ pump and remove the check valve...


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## Texan (Feb 21, 2015)

Ho talked to the guy today I think he's going to throw another check valve on the cold side of the tankless. Ive seen that work before but I think this time is different. Pumps in the tankless, but I did turn it off and the problem went away.


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## leakfree (Apr 3, 2011)

Had a house years back that another company did.2- 50 gallon heaters each one had a recirc pump tied into it,dual check on the service,overnight the hot would back up all the way to the kitchen sink,first thing in the morning hot on the cold side,then it would run cold.We checked everything looking for crossed lines or anything wrong,found nothing.Recirc lines were tied into the cold feeds and had checks on them,ended up trying dual checks instead of the spring checks and it stopped it with no visible loss of flow.Someone referred to it as"thermal creep",and that the pumps were creating enough of a pressure differential in the closed system to back the hot up into the cold past the checks.


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## rjbphd (Feb 5, 2010)

leakfree said:


> Had a house years back that another company did.2- 50 gallon heaters each one had a recirc pump tied into it,dual check on the service,overnight the hot would back up all the way to the kitchen sink,first thing in the morning hot on the cold side,then it would run cold.We checked everything looking for crossed lines or anything wrong,found nothing.Recirc lines were tied into the cold feeds and had checks on them,ended up trying dual checks instead of the spring checks and it stopped it with no visible loss of flow.Someone referred to it as"thermal creep",and that the pumps were creating enough of a pressure differential in the closed system to back the hot up into the cold past the checks.


Each one had pump tied to it. And tied to the cold supply?? .wtff?! Def not done by hdyronic heating company


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## leakfree (Apr 3, 2011)

Not done by me or the company I worked for,but the dual checks were what seemed like the quickest fix which is what the H/O cared about.


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## Texan (Feb 21, 2015)

The more I think about it I wish I had thrown a check valve on the cold side of the tankless just for sh!ts and giggles. Only reason I didn't do it was the water would get hot at the ks again after two minutes that was like 80' from the tankless, and it would come out of the tap warm within 3 seconds. Thats a fast creep if thats what it is.


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## OpenSights (Mar 23, 2015)

This is pretty much out of my league AFA understanding the HVAC side of mechanical.... The last plumber I worked for had a few accounts that used the apollo style heating system. (Might be a good idea for southern States, but not for Michigan and other northern states.) IDK how many I've replaced over the years, but the check valve trick always confused me. Take out the old heater with no checks, next day, no heat call, install a check, sometimes it'd work, sometimes, no heat the next day. eventually we just started installing checks on both sides just so we didn't have to go back.


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## rjbphd (Feb 5, 2010)

OpenSights said:


> This is pretty much out of my league AFA understanding the HVAC side of mechanical.... The last plumber I worked for had a few accounts that used the apollo style heating system. (Might be a good idea for southern States, but not for Michigan and other northern states.) IDK how many I've replaced over the years, but the check valve trick always confused me. Take out the old heater with no checks, next day, no heat call, install a check, sometimes it'd work, sometimes, no heat the next day. eventually we just started installing checks on both sides just so we didn't have to go back.


Learn gravity hydronic heating system... how many pump or check valve(s)?


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## OpenSights (Mar 23, 2015)

rjbphd said:


> Learn gravity hydronic heating system... how many pump or check valve(s)?


I believe one pump in the heat exchanger. Usually the heat lines tied into the sides, but sometimes both hot and return were tied in at the top... those were always checked. Another thing I found odd about this system is on one property the maintenance guy would always have to bleed the lines even with the heat side closed when swapping the heaters out... the other 4 properties didn't need to be bled. 

I forgot to mention earlier, that without the checks on the HVAC side you'd get either just luke warm in the hot OR luke warm on the cold. They run these heaters full bore and an apt is lucky to reach 70 degrees in the winter. I never set the temp other than to just above vacation for testing. All the maint. guys knew to come back behind me and set it to max themselves. Three of the apt complexes are owned by a very well to do family... I keep on saying "I don't know how they haven't been sued yet. Only one of the four properties had mixing valves for the faucet side. During the summer I couldn't stand the HOT of the water, and I'll hold a chunk of copper in my hand to sweat it....

Edit to add: I've only worked on a few circ pump lines, and all but one were just R&R..... unless you count those stupid Bell&Gosset sleeve bearing pumps I had the delight of working on while in the motor business.


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## Michaelcookplum (May 1, 2011)

Had a job one time where hot and cold water were ran in a bulkhead to the kitchen sink and island sink. About 40' runs. Hvac guys also ran there duct pipe in the same bulkhead. In the winter time when the heat was on in the house the HO complained of this same issue. Cold water started cold for first few seconds then went warm for 30 seconds and then back to cold. We cut in 2 6x10 ceiling registers into the drywalled bulkhead to let the trapped warm air out. Problem solved! 

This house did have recirc line in it to the master but not to the kitchen or nearby the kitchen tie in.


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## Texan (Feb 21, 2015)

Thanks sounds just like whats happening. Going back next week to put.a check in at the cold side of the tankless. And if that doesn't fix it we will try to find where the pipes are and insulate better or move them.


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## bcpscott (Apr 16, 2015)

I'd bet the recirc line is running back to the heater next to your cold line going to the kitchen. Even if not underground in the same trench, it would be in the attic under insulation following the same path back.


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## Michaelcookplum (May 1, 2011)

So what happened when you went back?


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## Texan (Feb 21, 2015)

Mike, still no resolution. Never went back, she rescheduled with the office. Ill update when I do go back. She had some medical stuff going on, plumbing may have got pushed to the back burner.


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