[rames14]

I don’t know anything about the tankless water heater, but the furnace on ours exhibited similar behaviors. We looked at gas flow, sail switch. Finally had a mobile tech look at it. Took the whole furnace apart. Nothing. Finally, while putting it back together, he found the screw that holds the igniter was stripped. That also served as the ground. He installed a slightly larger screw, tightened it down and we have heat in Alaska.