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Note: I did not write this--it was copied from an email (from a source I trust) that claimed it was copied (and edited) from a Facebook post. If the original author is determined they will be credited appropriately. -Howard
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Furnace Troubleshooting by Timing
The wall thermostat must first make a call for heat. In effect, it closes a connection to the two blue wires on the furnace control board. The control board checks to see if there is more than 9.5 volts DC and that the sail switch is open. If all is well, then the control board starts the fan turning.
There are a couple of things that will auto-shutdown the system. The first is the sail switch. The fan must get up to 75% speed and the air will push a small switch's contacts closed. If it does not close, the system shuts down after 30 seconds. Time this. If it dies in 30 seconds, it is likely the sail switch.
The sail switch closing tells the control board that it is ok to ignite the burner. The furnace won’t wait for the 30 seconds timeout if the sail switch is confirmed closed in a couple of seconds. The furnace will start the ignition sequence. The fan will run for 15 seconds to purge the furnace of propane. The control board checks that the propane valve relay contacts are open. Therefore, if a shut-down occurs within 15-20 seconds after the fan starts up, the problem is likely the control board's propane valve relay.
If the relay contacts are confirmed open, the ignition sequence starts.
The module board is now ready to try to ignite a flame. It opens the gas valve, and for 7 seconds, tries to ignite the main burner flame. If your’e close to the furnace, you can hear the spark from the igniter. If the control module senses a flame, all is well. If there is no flame, the control module ceases trying to ignite the flame, and does another 15 second purge just in case there is any propane in the unit that did not ignite.
It will then attempt to ignite the furnace twice, going through the same ignition sequence.
After that, if there is no flame, the control module will de-energize the gas valve and cause the blower to run for 3 minutes and then put the furnace in a lock-out status. To restart you will need to turn the furnace off and then back on.
If there is no propane getting into the furnace (all else being ok), the sequence will be as follows:
1. Call from wall thermostat to request heat. Control board insures there is >9.5 VDC and the sail switch is open. If not, nothing happens.
2. Sail switch ok, fan turns on and the sequence begins.
3. Control module confirms propane valve closed; fan runs for 15 second purge.
4. First ignition attempt. If ignition fails, 7 seconds.
5. Begin second air purge, 15 seconds.
6. Second attempt at ignition fails, 7 seconds.
7. Begin third purge, 15 seconds.
8. Third attempt at ignition fails, 7 seconds.
9. System runs fan for an additional 3 minutes and goes into lock-up.
The times in seconds are 15 + 7 +15 +7 + 15 +7 + 180 = 246 seconds or 4 minutes and 6 seconds.
If it runs this long before shutting down then there is a propane problem, a control board problem (not opening the propane valve), or the propane valve itself.
If the furnace shuts down before this time, it is not from a lack of propane.
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Furnace Troubleshooting by Timing
The wall thermostat must first make a call for heat. In effect, it closes a connection to the two blue wires on the furnace control board. The control board checks to see if there is more than 9.5 volts DC and that the sail switch is open. If all is well, then the control board starts the fan turning.
There are a couple of things that will auto-shutdown the system. The first is the sail switch. The fan must get up to 75% speed and the air will push a small switch's contacts closed. If it does not close, the system shuts down after 30 seconds. Time this. If it dies in 30 seconds, it is likely the sail switch.
The sail switch closing tells the control board that it is ok to ignite the burner. The furnace won’t wait for the 30 seconds timeout if the sail switch is confirmed closed in a couple of seconds. The furnace will start the ignition sequence. The fan will run for 15 seconds to purge the furnace of propane. The control board checks that the propane valve relay contacts are open. Therefore, if a shut-down occurs within 15-20 seconds after the fan starts up, the problem is likely the control board's propane valve relay.
If the relay contacts are confirmed open, the ignition sequence starts.
The module board is now ready to try to ignite a flame. It opens the gas valve, and for 7 seconds, tries to ignite the main burner flame. If your’e close to the furnace, you can hear the spark from the igniter. If the control module senses a flame, all is well. If there is no flame, the control module ceases trying to ignite the flame, and does another 15 second purge just in case there is any propane in the unit that did not ignite.
It will then attempt to ignite the furnace twice, going through the same ignition sequence.
After that, if there is no flame, the control module will de-energize the gas valve and cause the blower to run for 3 minutes and then put the furnace in a lock-out status. To restart you will need to turn the furnace off and then back on.
If there is no propane getting into the furnace (all else being ok), the sequence will be as follows:
1. Call from wall thermostat to request heat. Control board insures there is >9.5 VDC and the sail switch is open. If not, nothing happens.
2. Sail switch ok, fan turns on and the sequence begins.
3. Control module confirms propane valve closed; fan runs for 15 second purge.
4. First ignition attempt. If ignition fails, 7 seconds.
5. Begin second air purge, 15 seconds.
6. Second attempt at ignition fails, 7 seconds.
7. Begin third purge, 15 seconds.
8. Third attempt at ignition fails, 7 seconds.
9. System runs fan for an additional 3 minutes and goes into lock-up.
The times in seconds are 15 + 7 +15 +7 + 15 +7 + 180 = 246 seconds or 4 minutes and 6 seconds.
If it runs this long before shutting down then there is a propane problem, a control board problem (not opening the propane valve), or the propane valve itself.
If the furnace shuts down before this time, it is not from a lack of propane.
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