I have been noticing the fan (I assume it is the combustion air fan, don't know if there is another fan in this thing) runs alot. After a burn cycle is done the red light goes out, and the fan runs for awhile and then turns off. But a few minute later the fan will fire up again, even though there is no call for hot water. Then it will do it again a few minutes later.
Is this normal? Seems like an awful lot of fan useage to me.
I do have a hot water recirc with dedicated line and check valve on the cold water inlet side of the return. However, this is a Redytemp that is on a timer (total of about 2 hours a day), and a manual switch. The pump is not running when I observe this behavior. However, the cold water inlet line can be warm if the recirc has been used recently. Not sure the recirc is causing the fan to run given the pump isn't on, but thought I should mention it just in case.
Maybe that check valve is interacting with expanding/contracting water on the cold side just enough to trigger the water flow sensor and false start the tankless?
Edit: this is the NRC-1111DVNG