As per the installation manual, the heaters should be checked annually for any debris in the venting, cleaning of the inlet filter screen and cleaning of the water valve. The water valve should be cleaned with white vinegar and then the pushrod inside the water valve should be lubricated with plumbers grease or silicon grease. The Bosch tankless water heaters should have a water valve rebuild done every 3 - 5 years depending on the quality of the water where the heater is installed. The water valve rebuild kit (WVKITCT) #7738001923 includes the metal retaining plate, 2 set screws, pushrod and a packet of lubricant. Call GlobalTowne at 888-726-9752 to order the water valve kit and other parts.
