Reset button for tankless water heater

need a meter to test circuit for damage

Test elements for short
http://waterheatertimer.org/How-to-test-water-heater-element.html

Make sure unit is wired correctly:
http://waterheatertimer.org/How-to-wire-Tankless-electric-water-heater.html

Gene
Water Heater Timers Save Money

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

reset circuit breaker fully off the on
power outage can call surge
check fuse on circuit board

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

The NC250 (N-0931M) Series ASME Tankless Water Heater is a commercial grade water heater and many people install the vent wrong. PVC CANNOT be used for venting. The NC250-DV-ASME is for indoor use only. Improper venting will cause the symptom you describe.

I believe you killed it,I've installed two units direct vented through side wall in Minnesota and the cold wind blew in flu and froze up units,water stopped running in houses so we were able to save

This happens with Nortiz heaters. They just **** out. Likely the installation is very bad, but the unit can not tolerate that and it just dies. I recommend getting a Bosch 2700 or 715. If you want great efficacy, get the C-800. But follow the instructions! If it is installed correctly and you have the CO2 levels adjusted when it is installed, you will be very happy.

overheat stat or fan

Power outage will reset Rinnai unit to that temperature. Read manual for more info.

My guess it need reset.Turn power off for five to ten minutes and try that.The heat may have mis fired for the code.

what is it doing, I would first check the inlet water screen and make sure that it's clean. shut off the water going to the unit and the screen is right after the shut off, unscrew it and clean it. replace and turn the water back on. you can ask for me again if this does not help