Our new build 2 story home is now 8 years old. We have a 75 gallon hot water heater (gas) with TACO 006-B4-1PNP hot water recirculator (w/digital timer). It has been WONDERFUL! I may write a sonnet! Sadly, it seems a grain from the sands of time has intruded upon my bliss and I need help finding it!

1st noticed hot water in an upstairs shower starts out hot and within a few minutes begins to cool to the point the mixing valve is turned all the way to hot and the water is lukewarm. Launched a full scale investigation and discovered the following:

Digial display on face plate of TACO pump is so faded it is unreadable, but the pump is definitely working. I turned it off one night and the next morning waited 3 minutes for hot(ish) water from an upstairs tap. I turned it back on that night and got hot(ish) water from the same upstairs tap immediately the next morning.

Hot water tank is not throwing any error codes and hot water taps in basement, kitchen, and downstairs powder room are fine.

Upstairs: After "much turn this on with this on...now turn this off but keep this on and turn that on..."

Hot tap(single) of MY sink is warm, not hot, but turns COLD when any other hot tap in that bathroom (HIS sink(single), bathtub(single), and shower(mixer valve)) is opened.

As long as MY sink hot tap is open and cold water is coming out, the other taps are immediately as hot as they should be and stay that way until MY sink hot tap is closed. Then the other taps lose heat and go to warm.

When the other hot taps are closed, MY sink hot tap immediately goes from COLD to warm.

I will absolutely call a plumber, but I want to get some troubleshooting ideas first so I know what to ask for!

Shut off either the hot or cold angle stop under the sink and see if the shower hot water is hot. Sounds like the sink faucet is allowing cold water to enter the hot water supply piping.

Sadly, no change with either hot or cold undersink angle valve closed. While I was down there I noticed the dedicated return line for the recirc system starts under this sink.

back check valve assembly

==============================================

"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

Is the back check valve assembly something I can test as a layman?

if, repeat IF, you have this under your sink it needs replacement

[www.amazon.com]

==============================================

"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

Unfortunately, we do not have that device. Thank you for linking that, though. I was able to learn more about how the various ways these systems are designed. Our Taco 006-b4-1 is a plug and pump controlled by a timer/aquastat located next to the water heater. The dedicated return line doesn’t have a sensor at the furthest point.

there is a check valve either built into the pump or in the piping near the pump

these checks 'often' fail with time



(the rectangular box with the diaganal arrow pointing into the left bottom corner)

==============================================

"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638