Installed a h/w circulating pump at the sink furthest from h/w heater. Pump runs when temperature drops to keep water hot. If pump happens to be running when toilet in same bathroom is flushed, there is a loud continuous banging noise. It's not a single bang as in "water hammer", but a continuous bang as in a pneumatic hammer until the toilet tank fills. However, if you open the sink hot water faucet, the banging stops.

Anyone have a solution? Pump made by Gould Technologies.

Do this:

1. Close and Open incoming water valve for the toilet. See if the noise continues

2. Also, when the noise is happening, go to the toilet, lift the lid and put your hand on the fill valve. Feel if it vibrates

3. Unplug the pump. Flush toilet. See if the noise continues

Let me know what happened

Milo