Lukewarm water when recirculation pump is off

BM2

Happy New Year everyone!

This has been a head-scratcher for me and every plumber who has visited the house. We have a large old home with a hot water recirculation pump adjacent to the water heater which I keep on a timer.

When we run the recirc pump, things are basically great and we have hot water around the house.

When we turn off the recirc pump, the taps do not get hot, only lukewarm (mid 90 degrees). Some rooms warmer than others. I have not tried running for hours but at least 5 minutes and the temps don't budge.

What's more, if someone is taking a shower in the attic, the other bathrooms do not have hot water, only lukewarm. Once the shower is complete the temps are hot again. (The recirc pump has been running throughout)

Any ideas why this is happening? The pump is sort of a nuisance and we'd like to do without it and be able to take simultaneous showers. Let me know if I can provide additional details.

heathead

Two things to check.

First if you should check for a check valve on or near the recircuaton pump loop. If you have a valve on that return line turn off the pump and shut the valve see if you get hot water though out after you bleed the cold water out. If you do then open the closed valve and if it is cold again your check valve is bad.

Second do you have any thermostatic shower valves? You could be getting cross over from a bad valve. It is basically taking the cold water and mixing it with hot water then noting is hot.

Larry Weingarten

Hi @BM2 , @heathead nailed it. Try a crossover test. To do this, shut off the pump and then the cold feed to the water heater, and open any hot tap. Does water stop flowing from that tap pretty fast, or does it keep running? If it keeps running a good stream, there is a crossover between hot and cold that you get to find and fix. Moen and some other valves have been known to do this.

Yours, Larry