How do I diagnose a hot water recirculation problem?

Question

We have 2 ganged gas water heaters in a 10-year-old house. Professionals installed them last year to replace the 10-year-old pair. I'm pretty sure they are hooked up to a recirculating pump.

This setup has worked great until a couple weeks ago when the distant bathrooms started taking a full minute or so to produce hot water (suggesting a recirculation problem). After warming up, they also intermittently go back to cool water (suggesting running out of hot water), but after continuing to run for a while will return to hot water instead of getting colder (suggesting that it didn't run out of hot water after all).

I have unfortunately little plumbing knowledge but I want to know if there's something I can do to fix this problem before calling a plumber. I already tried the obvious solution of increasing the thermostat on the water heaters but that did nothing (again suggesting not a problem with running out of hot water). The water heaters themselves usually stay idle with a blinking light indicating the tank is at desired temperature.

Answer 1

I agree, your symptoms seems to indicate the problem is the recirculation system, not the heaters.

First, locate the recirculating pump. It could be near the water heaters, or at the farthest fixture from the water heaters. Your most distant bathroom may be a good place to look first. Look under the vanity or other enclosed places for a smallish device (size of a closed fist or bigger) with two water lines and an electric line.

It may have a timer that is mis-set, it may be unplugged, or plugged into a dead outlet (perhaps a tripped GFCI).

Other possibilities would be a valve closed either near the recirculator or at the water heaters (if the recirculator has a dedicated return the whole way back).

If none of these lead you to the problem, you may have a defective pump, or a more subtle problem... it may be time to call a plumber.