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 Hot water coming from cold water bathroom sink fixture
Author: candyman (TX)

Some specifics at the front end:

Mfg: Barand, circa 2001 (for bathroom lavatory and tub shower fixtures)
Mfg: Taco, circa 2016 (whole house recirculating hot water pump)
Water source: filtered rainwater for entire house
Recent plumbing repairs: Replaced both heating elements and both thermostats in 85gal Marathon (circa 2001) HWH

Problem: After this week's HWH repairs (which required draining/refilling the HWH), water from the upstairs bathroom sink cold water faucet now comes out very hot for a while before finally getting lukewarm, then "cold". If I turn the tub/shower thermostat to 90degrees or lower this seems to help with water temperature at the sink.

ETA, also seems to be a problem with downstairs bathroom faucet.

ALSO....the cold water line entering the HWH (at top of tank) is hot.....

Questions: Could this be an age/sediment clog/coincidence situation with the shower valve? Is this considered a 'crossover' problem'? Could this be a recirc pump check valve malfunction or the HWH thermostats that were recently installed? Why does the water temperature problem happen at the sink? Since remedy may require cutting into the wall, should the entire shower/tub fixture be replaced, seeing as how Barand no longer exists? Thanks for any help!

Edited 1 times.

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 Re: Hot water coming from cold water bathroom sink fixture
Author: packy (MA)

it is probably in the whole house recirculating hot water check valve.
it may be a separate check valve or it my be integral to the pump.

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 Re: Hot water coming from cold water bathroom sink fixture
Author: candyman (TX)

Thanks, we've unplugged (wall plug) the Taco recirculating pump and so far the problems listed have resolved, although it takes several minutes and some gallons of water for hot water to get to the fixtures upstairs. Plumbers working on coming out to assess. I am hoping it is not the thermostat mechanism in the shower set.

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 Re: Hot water coming from cold water bathroom sink fixture
Author: candyman (TX)

Plumbers (all 3 of them) just left after some head-scratching and diagnostics. Best guess is a defective thermostatic mixing valve (?terminology) in the tub/shower set. We and plumbers are scouring the internet to find a possible replacement. Might require changing the entire valve unit for this shower.

Our Taco recirculating HW pump is also suspect, since it becomes very, very hot when plugged in. Taco has been unplugged for several days and everything is working like normal with that unit out of the equation. But right now we're only trying to change out the shower cartridge (unless we can't locate a replacement).The proverbial Pandora's box.

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