Without more info I would have to say you need to increase water flo through the heater. If you don't have enough water flo the heater will boil the water inside heater and shut down. The heater has a pressure switch that reads OK but you have by-pass valves that may be open or stuck letting too much water go by the heater. One on the pipes going in and out of the heater may have a valve bridging the two that need's to be 80-90% closed forcing water through the heater. Then there is another spring loaded disc inside the main water header that you can remove and clean or replace that does the same job only the spring controls the flow automaticly. Good luck and HAPPY NEW YEAR.
Answers & Comments
Without more info I would have to say you need to increase water flo through the heater. If you don't have enough water flo the heater will boil the water inside heater and shut down. The heater has a pressure switch that reads OK but you have by-pass valves that may be open or stuck letting too much water go by the heater. One on the pipes going in and out of the heater may have a valve bridging the two that need's to be 80-90% closed forcing water through the heater. Then there is another spring loaded disc inside the main water header that you can remove and clean or replace that does the same job only the spring controls the flow automaticly. Good luck and HAPPY NEW YEAR.