I just descaled a rheem tankless water heater, general maintenance that I do periodically. This time, after finishing, the heater will start to heat and then shuts itself down with an error code 65 (water control sensor/solenoid). Ive tried flushing again in case I dislodged a large piece of scale. Ive also turned unit off and ran hot water for 10 minutes in case air bubble was trapped near the sensor. Any other ideas I should try...? And yes, it worked just fine prior to the maintenance . ....thats what I get for doing routine maintenance

I think I would suspect a faulty sensor. Is that possible ?

Thats always possible White, however, everything worked fine prior to the descaling. Just seems like too much of a coincidence that the sensor would go bad at the same time....unless of course the descaling process caused the sensor to go faulty. I think Im going to have to get out the multi-meter tomorrow and find out what I need to check on the solenoid. A new water flow solenoid is about $135, I just want to make sure I checked everything I could before biting the bullet.

It does seem coincidental for sure!

Ttt for morning crew

I’ve had them apart a 100 times but never had a sensor problem. Can it be taken out and cleaned. I fight moths in the fan and burner. I’m a expert fan remover and cleaner

Pawnee, I was able to take the water control valve apart after work today and clean the internals. The descaling must have left debris in the gear/plunger that did not allow it to open and close as it should. It worked like a champ once reassembled and the hot water is flowing again. The missus wasnt impressed having to skip her shower before work this morning, but Im tickled to save $135....that'll buy me a couple bullets...