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I have an unrented mobile home with an oil furnace that

Customer Question
Hello Pearl, I have...

Hello Pearl, I have an unrented mobile home with an oil furnace that burns kerosene. Every fall (now) for the past three years I try to get the furnace to keep the interior around 50f. Same problem every time: furnace will trip the reset many hours after I get it going. This year I set up internet sensors to watch the thing cycle. Last night first frost and I see it cycled three times until midnight and bang it is now 42f in there. Several commercial service attempts with same results every time

Contractor's Assistant: Did you check the furnace's filters?

Filters removed at the moment

Contractor's Assistant: Do you plan on doing the work yourself?

As long as no one is living there, yes

Contractor's Assistant: Anything else we should know to help you best?

Flame sensor replaces twice, new fuel lines, full tank of fuel.

Submitted: 10 months ago.Category: HVAC
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Customer reply replied 10 months ago
Flame sense and fuel line were done by commercial service techs. I am being encourage to replace the burner but I see it works and heats while it is running so why replace the whole thing to shotgun it? Is there not a step by step process to find the real problem? Good CO detector nearby, flue seems ok, fan always comes on after a short repeatable delay, always seems to start after pressing reset... ??
Answered in 41 minutes by:
10/1/2017
HVAC Technician: Rick, HVAC Supervisor replied 10 months ago
Rick
Rick, HVAC Supervisor
Category: HVAC
Satisfied Customers: 24,624
Experience: 40+ yrs. experience as a licensed oil & gas technician.
Verified

Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your issue. First I’ll need some more info so I have a more complete picture of your situation.

Does the burner shut down when it is firing?

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Customer reply replied 10 months ago
Have never caught it failing while standing there. Part of the frustration :)
Customer reply replied 10 months ago
Have never caught it failing while standing there. Part of the frustration :)
Looking at the duct temperature cycles from last night, I see no partial cycles if that helps.
HVAC Technician: Rick, HVAC Supervisor replied 10 months ago

What's the brand and model of the burner? has the ignition transformer spark ever been checked?

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Customer reply replied 10 months ago
I will check it and reply. Probably an hour or less. Not sure on spark but parts changers have tried several times. Happy to check if you can walk me through it. (Career field service background medical and semiconductor industry)Have never caught it failing while standing there. Part of the frustration :)
Looking at the duct temperature cycles from last night, I see no partial cycles if that helps.
HVAC Technician: Rick, HVAC Supervisor replied 10 months ago

TRANSFORMER CHECK

You can check the transformer with a heavy (plastic handle) screwdriver, shut off the oil valve on the pump, swing the transformer/igniter back on its hinge and put the blade of the screwdriver on one terminal of the transformer and hold the tip 1/2" away from the other terminal and hit the reset button. If the arc doesn't jump the gap then the transformer is weak and should be replaced.

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Customer reply replied 10 months ago
Rick, Becket AF15
Isi or Lsi furnace division of lear
Model cnf80-po
HVAC Technician: Rick, HVAC Supervisor replied 10 months ago

Ok, also check electrode gap. Should be 1/8" apart, 1/8" ahead of the face of the nozzle and 7/16" above the centerline. Also check for cracks in electrode porcelain.

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Customer reply replied 10 months ago
Interesting, this morning it is running only for a brief time them kicking off. I see fire in the view port but not all that long. It ran just long enough for the circulation blower to kick on for a bit. Tries to restart itself and does. Each time runs a bit longer.
HVAC Technician: Rick, HVAC Supervisor replied 10 months ago

If the burner shuts down (prematurely) then fires up again on its own with no reset then you have to look at the fan/limit control.

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Customer reply replied 10 months ago
Ok I have a silver honeywell box with a white plastic manual/auto push pull. That looks to be running off a sensor above the fire box and one leg of the blower power is going through it. How to check? This honeywell Box looks fairly new.
After two initial resets in cold trailer this am for you, this has been staircasing it's growing run time. Now just running.
Yesterday it started on initial reset and ran continously until I left the trailer.
HVAC Technician: Rick, HVAC Supervisor replied 10 months ago

You have to check voltage on the burner side of the fan/limit. If it's cutting out while there is a call for heat but before it reaches the hi limit pin then the control is defective. Another possibility is a bad thermostat or thermostat wiring so we always jump out the thermostat at the burner when troubleshooting

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HVAC Technician: Rick, HVAC Supervisor replied 10 months ago

Ok, but all of the above still applies. High limit keep the heat exchanger from overheating.

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Customer reply replied 10 months ago
A-Springing sound at burner, could that be air in fuel line? Or normal pump noise? I see no flicker in flame to my eye.
B- this time burner stopped but blower still running. Then burner started again before blower shut off. Normal??
C-Ok steps to take:
1- jump tstat during testing
2- with fuel off, knob ccw until it falls off, tip back head and check spark and electrode distances.
3-check voltages on fan/limit.
Did i miss anything?
Does fan high limit normally cycle the burner off on a long heat cycle like warming this freezing trailer back up? Or is it purely emergency shutoff? Curious if we are not moving enough air across the heat exchanger??
HVAC Technician: Rick, HVAC Supervisor replied 10 months ago

A) I have no idea what the noise you are describing mght be and no way to tell from here
B) yes, blower will run as long as there is a call for heat once the heat exchanger heats up. Burner will shut down when it reaches limit temp then back on again after blower drops heat exchanger temp
C) yes

Yes limit cycles burner off on a long cycle. It's perfectly normal

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Customer reply replied 10 months ago
A-Ok inverse question, could one hear air in the fuel line as the pump is running?
B/C- ok sounds normal.
Perhaps the issue is at startup when it sits for a few hours. What will make it trip the reset, forcing a manual reset?
The trailer reaches setpoint and it has not shutdown as expected. I will do breakfast and check back in a few hours. This is exactly what happens. It seems ok but then I find the trailer ice cold and needing another reset.
HVAC Technician: Rick, HVAC Supervisor replied 10 months ago

A) no

Lockouts happen with ignition or control failure. Of over looked is the cad cell socket and wiring. You said the cad cell had been replaced, what about the socket?

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HVAC Technician: Rick, HVAC Supervisor replied 10 months ago

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