We had some rain that blew sideways yesterday and tripped our outdoor GFCI which is connected to our tankless gas water heater. The orange light is showing and we can’t reset the outlet. I’ve turned off the main breaker feed to the water heater to avoid any more damage. We are shivering in our showers and need a solution.
Model for water heater: Takagi AT-K5U-OS-N at AC 120v
Disconnect the load wires from the GFCI. Turn the breaker back on and try to reset the GFCI.
If it cannot be reset, the problem is in the GFCI. This is common for GFCIs mounted outdoors. You will need to replace the GFCI, and you should try to make it more weatherproof. It needs a good weatherproof cover (UL listed for that purpose) or better yet, relocate it indoors.
If the GFCI can be reset with the load disconnected, then you have a ground fault in the load (i.e. the water heater, the wiring to the water heater, or any other outlets that may be sharing that circuit).
Since you suspect moisture as the cause of the GFCI trip, use a hair dryer to evaporate the moisture in the GFCI box. After your hot shower, relocate the GFCI indoors.
Get that water heater onto its own dedicated circuit asap. Putting a GFCI outlet - especially an outdoor outlet -- in front of it is a bad idea and a code violation.
If this is a 120V point-of-use water heater, strongly consider replacing it with a 240V unit.
Even the control/ignition circuit for a gas water heater should dedicated to that purpose.
See also Point-of-use tankless water heater electrical connection
