R
Rogelio
I just had installed a Navien NPE-2 with built in recirculator pump. I have a dedicated return line. The check valve for the recirc is built into the unit; a spring check valve was placed on the cold line (per the manual) after which there is an expansion tank (on the cold line) in a T junction which feeds into the cold water inlet of the unit.
Whenever the cold water on any fixture is opened and closed quickly, there is a clunk. This happens regardless of when the recirc is on. It does not happen with hot water. This never happened before with our previous water heater — we also had a recirc pump (with a spring check valve feeding into the bottom of the tank) and cold water fed to the top with the expansion tank on the cold line (albeit no check valve on the cold line like in the tankless,as it’s not necessary per code or per install requirements).
Never had “water hammer” before the tankless. I even tried an arrestor at fixtures and the clunk occurs just as loudly near the garage (where the tankless unit and check valves are) in the same manner as without using arrestees. Municipal water pressure is 70 psi and the expansion tank is set to 40 psi — though this is irrelevant because the cold line is isolated from the expansion tank when cold water is run due to the cold spring check valve. The installer said this exact same clunk sound behavior took place with another client and he tried removing the cold check valve and the clunk when using cold water / closing went away. I believe though that no check valve in a recirculating tankless setup makes some warm backflow go into the cold line and may cause reverse pressure to trigger the fan (post purge) when the unit detects a flow change because cold water draws out pressure.
Has anybody seen this before or have a solution that isn’t simply installing a pressure relief valve (which I don’t think would change the clunk due to the spring check on the cold)? I’ve heard clunks on swing checks but this sound and it activating the clunk when the cold only valve is opened/closed (more when closed) doesn’t fully make sense to me.
Whenever the cold water on any fixture is opened and closed quickly, there is a clunk. This happens regardless of when the recirc is on. It does not happen with hot water. This never happened before with our previous water heater — we also had a recirc pump (with a spring check valve feeding into the bottom of the tank) and cold water fed to the top with the expansion tank on the cold line (albeit no check valve on the cold line like in the tankless,as it’s not necessary per code or per install requirements).
Never had “water hammer” before the tankless. I even tried an arrestor at fixtures and the clunk occurs just as loudly near the garage (where the tankless unit and check valves are) in the same manner as without using arrestees. Municipal water pressure is 70 psi and the expansion tank is set to 40 psi — though this is irrelevant because the cold line is isolated from the expansion tank when cold water is run due to the cold spring check valve. The installer said this exact same clunk sound behavior took place with another client and he tried removing the cold check valve and the clunk when using cold water / closing went away. I believe though that no check valve in a recirculating tankless setup makes some warm backflow go into the cold line and may cause reverse pressure to trigger the fan (post purge) when the unit detects a flow change because cold water draws out pressure.
Has anybody seen this before or have a solution that isn’t simply installing a pressure relief valve (which I don’t think would change the clunk due to the spring check on the cold)? I’ve heard clunks on swing checks but this sound and it activating the clunk when the cold only valve is opened/closed (more when closed) doesn’t fully make sense to me.
