dano73 wrote:
There are no webs in the burner tube. I don't see a thermocouple, is it part of the igniter electrode?
Yes, it probably is part of the ignitor. When the flame hits it there is a millivolt signal sent to the card.
I went through all that with mine. I checked all the connections, cleaned everything, replaced the ignitor and in the end my board had to be bad. I replaced the whole water heater as I didn't want to chance buying more parts for an old water heater. You say that you replaced your card with a known good card but maybe it isn't good?