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We had a power outage and my tankless water heater (Model #

We had a power...

We had a power outage and my tankless water heater (Model # AT-K4UOSN) controller doesn't turn on I do have power to the electrical outlet

Contractor's Assistant: How long has this been going on? And how severe is the problem?

It happened this morning so there is No hot water

Contractor's Assistant: Do you plan on doing the work yourself?

Yes

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Answered in 3 hours by:
3/18/2018
Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 9,695
Experience: Retired HVAC/ Electrical & Boiler contractor. Industrial
Verified

Hello, it is most likely that the power surge (spike) that came with the power outage damaged the printed circuit board inside your water heater.

.

Take close up, exceedingly well focused photo's of the wiring diagram glued inside water heaters service panel and I will mark it up with trouble shooting instructions.

Use the 'add files' link next to your send button to get the photo(s) to me.

.

We can go from there with training, coaching and diagnosis.... without a time limit, In depth with as much detail as needed .

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When we finally get the situation solved, please select the 'finish and rate your expert link' near the top of your page and click on it.

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Thanks, click here please

If you have 120 vac between the 120 volt connections to the printed circuit board, red marks... and if you unplug each of the sensors marked in blue, and measure resistance (set multi meter on OHMS) across the sensors and do not get an open, or a completely shorted circuit, the printed circuit board is most like bad, PCB

Inspect the PCB for any corrosion or burn marks, let me know what you find.

We can go from there as needed. If this seems to be beyond your skill sets, tell me which direction you are from the center of the nearest city and I will locate a well rated service outfit for you.

Note: the average life span on these is in the 10 to 15 range, if the water heater is older than that, replacement will be a good idea.

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Customer reply replied 4 months ago
Hello
No120 at the red marks and the blue marks show 5 ohms
No burn marks on the board
what about the surge box looks like ther is 2 fuses in side but can't tell if they are blown out
it has 120 going in to the top of the surge box but not out of the bottom and the fuses are in between

Hello again, remove the fuses and test them with an ohm meter ...do not try to test them in place.

If the fuses are blown replace them, and tell me how it goes

Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 9,695
Experience: Retired HVAC/ Electrical & Boiler contractor. Industrial
Verified
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