I have a mobile home furnace Intertherm #1378. The pilot light is on, but the burner will not light. The thermostat clicks on and everything seems to be running properly, but there is no flame. Last year I had the motor replaced and the relay switch. What could be wrong? Is there a gas valve that is not opening properly.

There should not be a pilot on a direct vent furnace. When you turn up the thermostat for heat the 1st thing to happen is a venter motor should start, it should vent for approximately 45 seconds, the air switch will verify a vacuum in the burner box, then a spark igniter should start clicking to start the pilot, then the flame rod will verify the pilot, the igniter will stop clicking, and the main burner will ignite and remain on until the thermostat has satisfied the set point. These guideline steps must be satisfied before the controller advances to the next step. The 1st step is the venter motor running, sometimes the motor will stick over the summer months, spin it manually to unstick it. PS, nothing runs if the fan door cover is open, as that shuts down the power to the whole furnace.

by igniter I assume you mean the thermocoupler. are you turning the control button to run after you light the pilot light? Normally when those furnaces quit it is the thermocoupler that has quit. Get a new one and leave it in the furnace compartment as a spare.

Furnace burner and heat element are not the same. I think the fan time delay, a sensor that turns the fan on when this sensor senses heat, is shot and needs replacing, for a furnace type heat ( gas heat)

see this causes and fix it. God bless you
f there is no heat, check the electrical service panel for a burned fuse or tripped breaker. Relight the pilot light (see below). If there is not enough heat, adjust the burner air shutter (see below); and clean the burner ports (see below).
If the pilot light does not light or does not stay lit, clean the pilot orifice carefully with a toothpick, test the thermocouple and replace it if it is faulty (see below).
If the flame flickers, adjust the pilot (see below).
If there is an exploding sound when the burner ignites, adjust the pilot to a higher setting and clean the pilot orifice and the burner ports.
If the burner takes more than a few seconds to ignite, clean the pilot orifice and adjust the pilot light.
If the burner flame is uneven, clean the burner ports. If the burner flame is very yellow, clean the burner; open vents in the furnace room to provide more air; adjust the burner air shutter.
If the furnace makes a rumbling noise when the burners are off, clean the burner and adjust the burner air shutter.
If the air is too dry, wash or replace the evaporator pad if you have a humidifier; test the humidistat; and adjust the water-level float to raise the water level.
If some rooms are too cool and others too warm, the distribution system may require balancing. Refer to the Forced-Air Distribution Fix-It Guide .

If your pilot light is lit then I would first check your thermostat. Make sure it is on heat setting and fan is on auto, turn stat up to where it should be calling for heat. If you don't get burner to light remove front cover from thermostat and see if it has a mercury switch, if it does move temperature selector up and down and see if you can see a spark in mercury switch vial. If y ou cannot see a spark remove screws that attach t-stat to base.Remove carefully and disconnect wires that go to r and w terminals on stat base. Temporarily connect these two wires together. This should make burner light if you have power to thermostat. If burner does light disconnect wires and replace thermostat. Also if you have a volt meter check across these two wires and see if you have power there. Should be around 24 volts a.c. If your thermostat has a fan on setting try that. If fan runs you know you have power to furnace The gas valve needs 24 volts to operate and inside the electric control box in furnace there is a transformer to step down 110-120 supply voltage to 24 volts. If transformer is working you should be able to hear a low buzz or humming sound. You can also check across gas valve terminals when t-stat is set for heat, you should read about 24 volts. If you have 24 volts to gas valve and it is not opening then you need to replace gas valve. The main purpose of the limit switches is to turn blower on when temperature in heat exchanger reaches fan on temp,shut off blower after burner shuts off and heat in heat exchanger reaches fan off temperature, and limit if temperature exceedes set point without blower coming on. I hope this helps you. Thanks

If your friends heater has a pilot light but no burner I would be inclined to change the gas valve. You need to get the proper gas valve for mobil homes. They require a two stage slow opening valve. Make sure it is set up for the right type of fuel. If possible have someone with experience working with gas to help you with repairs. I hope this helps you some. Thanks

Check your exhaust pipe for blockage, Make sure pilot light is located just above or below the burner. Make sure that there is a good supply of air going to the burner and that the intake pipe (if it has one) is not restricted. A furnace that old needs to be replaced what ever you find. You could have a cracked heat exchanger.

Check to make sure the roof vent is not covered over with snow.
Very deep snow can block the intake to the furnace. You may need a ladder and a broom (or shovel) to clear the snow.
Hope this helps.
Matt

the blower on my furnace keeps going on and off when i turn the furnace on .ichanged the snapdiscs no change changed thermocoupler and therostat still no change whats my problem