Things have been going smoothly for about 4-5 weeks with my summer settings, 3 teeth, 4 air, timer set at 1.5 minutes on the half hour and .5 on the 15 minutes. My oil unit is in series with the EFM so there was some gravity feed going on between the two units. I have one flow check valve on the first floor zone that sometimes doesn't stop the gravity feed. Yesterday my first floor radiators were warm (gravity feeding again) Last night I closed the valves for the zones and one in the piping between the two boilers. Stopped all of the gravity feeding but left a path for any make up water to get between both boilers. This afternoon my son called me at work to tell me we didn't have any hot water. The fire was out.
My guess is with all of the water circulation between boilers and zones the EFM was running on more than just the timer. When I cut off all of the flow there wasn't enough timer to keep the boiler lit. Here's my question (finally), Is it better to add more run time on the timer or add more air? I'm concerned adding more air will make the fire burn lower in the pot and damage the worm. I just re-lit the boiler and moved the timer up to 2 minutes on the half hour. It's burning more coal that way but I'm not sure if adding more air will solve the problem. Thanks for any advice.