Oil fired intertherm trailer furnace would kick out during the night . I Had replaced the fuel pump as the seal let go ,the cad cell ,the protector relay , the cracked air guard, the fuel filter 3 times, the first was slightly dirty and the nozzle 3 times. each time I worked on it it would be fine for a day or two and then it would shut down again.

In the links

M Series Furnace - Mobile Home

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19, Filter - Furnace, 668356, F-30, $16.28. Filter Kit - (Includes filter and ... Plate - Ridge (MGH-055, MGH-065 & MGH-068), 223070 223490, - -. 33, Panel - Air ...

Intertherm Furnaces

Intertherm https://intertherm.net > intertherm-furnaces
Intertherm Furnaces MADE SPECIFICALLY FOR MANUFACTURED HOMESComfort You Can FeelFurnaces are measured using AFUE (Annual Fuel Utilization Efficiency).

Filter for Intertherm Modular Trailer Furnace

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Could be the photocell (CAD cell) on a residential boiler, or a fuel problem ie dirty fuel filter, oil lines losing prime.

My first guess would be that it sounds like a clogged oil filter, air in your fuel line, is piping overhead, or leak in a fitting or connection causing it to loose it's prime when running.

I have also seen primary controls that are faulty do this, watching the complete cycle of the run time will give you more clues as to when the control actually locks out. Does it lock out during the run cycle as the boiler reaches temp.? If so,check for oil line and suction issues as stated above.

If it locks out on start up after reaching boiler set temperature, if hitting reset right away burner doesn't start and lock out occurs with no motor engaging, check motor (Note: Some motors when HOT will not kick in when powered, but after they cool down naturally they start, motor shaft may also be bound up tight, replacement is necessary) if burner motor spins but does not fire, check for fuel flow to the nozzle, be sure oil is pumping to the nozzle, if it is, clean cad cell eye, and check transformer for spark, if all is good.. replace primary control.

Disclaimer:
Of course all this information is technical troubleshooting information and should be performed by a Licensed Technician, not knowing how to properly test for flame failure can cause injury, fire or worse! Consult a technician in your area if you are not proficient at oil burner repair!

Does the power pack deliver enough volts? Is the gap on the electrodes too wide? Is the burner spud clogged? I believe it should put out about 10,000 v. is the cad cell clean?

Ok. First of all what I'm understanding is that your primary burner control is tripping off... generally this has nothing to do with getting hot unless it is mounted close to the burner (the primary control is a circuit board that read resistance from the photocell -cad cell- to prove the flame...and if it gets hot, like any circuitry, could cause problems). If it is mounted close to where the actual controller is getting hot, then build a spacer out of sheet metal. If it is not tripping because of heat, its tripping from not reading the light of the flame via resistance... hence you have to lift the Ignition transformer to access the cad cell, & clean the glass front. (Cad cells doen't usually go bad) Pull the burner, and make sure it has the right nozzle rated on the burner assembly and furnace tag. The nozzle has a gallons per hour & spray pattern degree & number representing solid, hollow, semi-hollow, etc. I recommend semi hollow if you can't find any info on it, but make sure the gph correlates with the btu's rated on the furnace. The electrodes of the ignition transformer need to be positioned correctly for proper ignition. Make sure the fuel pump is tied to a two pipe system so the pump takes no time to prime. Supply & return should be piped with 3/8 copper flare fittings with no leaks. Also make sure the inline fuel filter cartridge is cleaned.
Now if the motor is tripping the motor reset, then it is trying to overcome the resistance of the pump...a 2 pipe system will help this, & making sure the motor is not mounted crooked. Take an amp draw on the motor while it is running and comparing to RLA rating on the motor tag to your actual amps can show you a lot.

It has an ignition control problem. Check the ignition transformer, relay, and the fuse.

The oil filter is usually located by the oil tank.Should be in a steel container painted red or blue.
Follow the fuel oil lines from the tank to the heater.
There may be a small filter located where the incoming fuelline goes into the pump.

If it is oil fired furnace I would change the nosel and filter and make sure the electrodes are set right.

Web page or the unit door covers , Intertherm are mostly added to trailer homes and check out a trailer home supply house.

check your cad cell. replace this. it is not detecting a flame. replacing the cad cell will fix your problem. when it shuts down it goes into lockout.