The oil furnace works fine all day and evening, then overnight I have the programmable thermostat lower the temperature at 11pm. But every morning at 5am when the thermostat tries to turn the temperature back up the furnace comes on for 45 seconds and shuts off. I go to the basement take off the panel. The box has a red light flashing. I push the reset button on the box, the furnace starts immediately and runs OK until the next morning. I've also had similar problems 5 or 6 months ago, had to call repairman twice and he said that he replaced almost everything he could replace. And it worked til now.
Something similar happened to my gas boiler. It was a problem with the ignition electronics. Every night, when the thermostat was lowered, the circuit board would cool down and a solder connection would come loose. Sometimes the board could be wiggled to make the connection again. Eventually I opened it up and identified and fixed the loose solder connection.
The ignitor box looked something like this:
Program setting turns heat off
Program setting tries to start furnace
Furnace runs for 45 seconds
Furnace shuts off - trips breaker behind the panel.
Reset breaker - System runs fine.
- Last time this happened, the repair guy took the shotgun approach and replaced almost everything.
So rather than knowing exactly what broke, we know that it is included in 'almost everything.'
(I am jealous that my boss will not just let me replace things until it works.)
Does the furnace make heat for 45 seconds, or just run the fan? I bet just the fan runs.
I am going to guess that something gets cold during the night, the furnace then tries to start-up in the morning.
The fan runs for a few seconds, the furnace senses the airflow, signals the oil pump to start.
The pump is cold, the oil is cold, the nozzle is cold.
The pump tries to start, but it is stalled.
This blows the breaker, but it also warms up the motor.
You go down, remove the panel, push the breaker button, the fuel pump is now warm and willing to run.
The heat comes on, the furnace, the pump, the oil, the pipe, the nozzle all run enough during the day that things are fine.
Then they shut off at 11pm, get cold, the thermostat tries to start the furnace the next morning ...
The question is now - what really did get replaced 6 months ago?
When the repair guy/woman was out at the time of the repair did the current draw of the motors match those of the ones that were recorded in the past, or at least the ones on the motor nameplate?
There becomes a question of if the problem really was fixed during the last service visit.
My suggestion is to get a logging amp/volt reading on the motors for a couple of days. I expect that the result will identify your problem.