Furnace problems

[usinmich1998]

I have a 1980 Dodge Starcraft with a suburban furnace.  The blower works but it will not ignite.  I just replaced the circuit board and can see it sparks.  It just will not ignite.  Any help would be appreciated. 

 

[John From Detroit]

Things that can keep a furnace from lighting, Note, skip to 4, then skip 5

1: Bad thermostat (yours is good, or it would not spark)
2: Bad sail switch (Yours is most likely good, see above)
3: Bad mother board (See above)
4: Bad gas valve (Solenoid),  4B: Gas turned off 4C Bad regulator
5: Improper igniter adjustment (But you see it sparking so not this is low on the list)

6: (PRIME SUSPECT) Clogged burner or orifice  Take the burner assembly apart CAREFULLY and clean it out

To check mother board, In fact to check the first 4 items measure voltage at the solenoid coil, 12 volt good, zero volt bad

5 You saw it spark

4 is a bit tricker
 

 

[rtaylor]

Low Voltage will cause your furnace not to ignite also if haven't had one apart yet and you don't have the new gaskets I wouldn't recommend taking the burner apart. One screw up and carbon monoxide can leak into the living area. I applaud DIY but some things should be left to the Pro's.

 

[Gary RV_Wizard]

Since you are seeing a spark and hearing the fan, the blower sail (interlock) switch is OK and probably the new circuit board as well (but see LP valve item below). T-stat is also OK if the furnace is attempting to start.

The basics of combustion is fuel + air + spark. You have the spark, so what about the other two? A furnace gets its combusion air from outside, so make sure the external air inlet is not clogged (bee's nest, spiders webs, etc).  And check the exhaust tube while you are at it. 

Making sure the circuit board has opened the LP supply valve and that LP is actually flowing can be difficult in a furnace, where most everything is enclosed.  I don't have any good suggestions on that, but maybe someone else will.

Have you verified that other LP appliances are getting gas? If not, your LPG detector may have closed the main feed safety valve or there could be a problem with the regulator or tank. But if the other LP appliances work, you can rule those out too.