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.