I changed the igniter first. Local parts man believed (99%) this would be the fix based on the appearance (arcing) and probable age (probably original). Relatively cheap first try too :^) Still doesn't always light off. Cycles the igniter 3 times, then goes 'to sleep' just as it's supposed to (I'm told). Power off - then back on - try again.
Is the ignition/control unit next ?
I do have 24v to the ignition unit, but I don't get 24v output to the gas valve. At least not every time. One time, when it finally opened, it was toward the end of the igniter cycle (it was cooling down). Is the gas valve on a time delay, or should the valve be powered immediately ? How does the control unit know when it's time to open the gas valve, since there's no temp sensor at the igniter.
This wouldn't be so frustrating or hard to diagnose if it wasn't an intermittent problem. (we hate those on aircraft too !!!) Usually, circuit-card controllers either work or they don't. They don't usually "kinda" work.
Thankfully it's not cold around here right now (Cincinnati area) Hate to have this sucker completely give up the ghost when it gets colder.
Watta y'all think...