The yearly oil furnace inspection my wife ordered included a switch to a smaller fuel nozzle. Performance improved (it was short-cycling) but the next day the furnace cut out and would't come on again. She called the people back and this time a crew of 3, after four hours of effort, get it working and chalk it up to "a bad transformer."
But yesterday it wasn't working again, so I looked at it. Nothing nada dead - not even a click from the control relay. I check the thermostat and there's 24 volts AC that switches to 0V when it calls for heat.
It is a 5 year old in-floor furnace that appears to be in good shape. I pulled the air circulation blower and beneath it found what I suspect they replaced and called a transformer - a Honeywell control module that has an input for the flame sensor and seems to control the whole shebang - and appears to be brand new. All connections are good but the red button on the top is up and resetting it returns the furnace to operation only to have it stop again after a few hours.
There's a small spring loaded trap door in the cast iron firebox/heat exchanger that allows me to see the flame.
I suspect an air/fuel mixture problem either causing a flame out (can't run it for hours with the inspection port open) or failure to reignite. flame is blue/yellow
My questions are how is the flame mixture adjusted - by flame color? There appears to be a sleeve around the burner assembly with a series of rectangular holes so that moving the sleeve would open or close the air intake. How does the flame sensor work? Is this something that requires a probe to be placed where it senses heat like a thermopile or light like a photocell? I couldn't see the actual sensor just the wires to it.
What should I be checking and can I tinker with the fuel mixture in safety? (I'm a retired electrical engineer - and good at repairing things)
And do these guys seem competent based on what I've written?