Sensitivity trainer and plumber of mens souls
We have the SAME nightmare issue- loud knocking noises in the pipes when the recirculating pump of the Noritz tankless WH turns on. No noises when hot water is running without recirculating pump on. It’s driving us crazy. Has there been any resolution? We have expansion tank, all kinds of check valves & the knocking noise is still there most heard in the wall of Master Bedroom shower. It’s not water hammering. The knocking noise is strictly limited to when the recirculating pump turns on (actually, when there is NO water being used!). Plz help. Several plumbers (including the installer) don’t know what’s causing it. I’ve already paid thousands of dollars. 3 Noritz WH were changed- all the same! ((
This knocking is due to the line being held too tightly to the studs... The copper line or pex line is expanding length wise and must move slightly during expanding..... you have to loosen the pipe straps and it should go away,.....if it goes up a wall to the second floor its gonna be impossible to do , if your walls are finished in the basement you are gonna have to try to locate the area the noise is coming from and cut drywall to locate the little strap that needs taken out.....
good luck ..