I installed an on demand hot water heater 9 months ago Rheem brand. Over the past 2 weeks when I have tried to run bath water I could only get a few seconds of hot water. I unplugged it the first time and it seemed to heat the water again but last night it did the same thing. I wasn't able to get anymore than a few seconds of hot water. I have only had this issue with running a bath, not a shower. Does anyone have any ideas?
Somewhere inside there is a water pressure or flow sensor that turns the heater on. Check that to see how well it is working. Clogging with sediment is not unusual.
The good conscientious technician or serviceperson will carry extra oils and lubricants in case the new pump did not come with oil or the oil was accidentally spilled, so the service call can be completed without an extra visit.