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Do I need some kind of heat loop?

BoonBoon Posts: 235Member
Hey folks. We have a single-arm kitchen faucet on which the cold side draws warm water when we turn on the cold. Eventually it runs cold. After it runs cold and we turn off the water for a few seconds, turn it back on, it stays cold for a few seconds then warms up for 10-20+ second And then finally goes cold again.

It’s a Grohe faucet and I’m outside the US so it was easier to get a new faucet than import a cartridge. The new faucet has the same problem!

I think I must be getting hot water from the inlet of the tank. I don’t know how to stop it. No room for a check valve and expansion tank. Any thoughts appreciated.

DIY'er ... ripped out a perfectly good forced-air furnace and replaced it with hot water & radiators.


  • ratioratio Posts: 1,930Member
    Any chance you've got a bubble of air in the tank? That might try and push hot water back in to the supply line.
  • Larry WeingartenLarry Weingarten Posts: 1,461Member
    Hi, Can I assume there is a record line? If so, the differential pressure it creates could be involved in this problem. My experience is that Moen and Grohe can allow a cross connection. You can test for it by shutting off the cold supply to your water heater and opening a hot tap. If it keeps running, you'll know cold is leaking into the hot side. The permanent fix is likely to replace the faucet with another brand. :#

    Yours, Larry
  • BoonBoon Posts: 235Member
    Thanks. I’m not familiar with the phrase “record line.” Was that an autocorrect? I’ll do the isolation test when I get back to the house.

    I can’t kmagine there is an air bubble but I’ll explore that, too. Not sure how I’d eliminate it.
    DIY'er ... ripped out a perfectly good forced-air furnace and replaced it with hot water & radiators.
  • hot_rodhot_rod Posts: 11,259Member
    recirculation line. What about a thermal expansion tank on the water heater. Any increase in HW pressure will push into cold side.

    Or another single handle valve is crossing?

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • BoonBoon Posts: 235Member
    edited June 2018
    Ok. No recirc line. I did the crossover test and indeed there is crossover within the faucet. With the hot water supply off and the faucet turned on hot I get water. Wouldn’t you know I replaced the Grohe with a Moen. Dammit!

    As I’m understanding this now, I either install a backflow preventer and expansion tank or I buy a Delta or Koehler or other brand. Does that sound right? I’m not excited about throwing more money at this, especially if buying a Delta or other doesn’t fix it.
    DIY'er ... ripped out a perfectly good forced-air furnace and replaced it with hot water & radiators.
  • ratioratio Posts: 1,930Member
    Shouldn't need to go all the way to a backflow protector, a simple check valve would stop the reversion. Don't know what to do about an expansion tank, although I've seen any number of weeping TP valves...

    Maybe a swing check with a small hole drilled though to relieve the expansion pressure?

  • BoonBoon Posts: 235Member
    The more I’ve looked into it, I’m convinced it’s hot water flowing back into the cold side. I kinda meant check valve. I’ll look into that.
    DIY'er ... ripped out a perfectly good forced-air furnace and replaced it with hot water & radiators.
  • HenryHenry Posts: 888Member
    Most probably, the cold water tube in the tank has failed. I have Grohe kitchen faucet and have no problems. But I have seen a few cold water tubes fall off.
  • Larry WeingartenLarry Weingarten Posts: 1,461Member
    Hi Boon, That was a late night foggy brain auto-correct. :# If you have a Moen in place now, and if it can accept the Moen 1225 plastic cartridge, that will correct the cross connection. B)

    Yours, Larry
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