Good morning, I'm new at this forum and have a question regarding my central heater. My Crossroads 5th wheel gas heater will ignite, but after about 5 seconds it goes off. I'm not sure if I'm in the right section, but any any advise would be appreciated.
central heater
- Thread starter jeff60
- Start date
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Alfa38User
Well-known member
- Joined
- Oct 4, 2007
- Posts
- 6,678
Hi and Welcome!!
This section is fine!!
For your problem, it would seem that the igniter/flame detector in the furnace is not functioning as it should. (This part does the both jobs.) You may have to remove the furnace to do much but I would check the wiring between the detector itself and the wire connection. Trace the wire and remove the connection at the circuit board and clean it well, both the wire end and the connection on the board, and then reconnect. You may have to replace the igniter/detector if cleaning and correct placement fails.
Theory: To detect the flame the igniter/detector has to sit in the flame. In the ignite mode, the igniter will flash 3 times and ignites the gas. When the flame ignites, the detector portion generates a very small voltage that is picked up by the circuit board during that 5 second period. If the flame is not detected then the furnace (or any other gas fired appliance) will shut down as a safety precaution. Since the voltage is very small, any corrosion etc. can prevent this happening.
You should find this article from the library helpful...
http://www.rvforum.net/joomla/index.php/16-rv-how-tos/333-furnace-troubleshooting
The fridge, the water heater, and the furnace all function similarly when operated on gas (propane).
This section is fine!!
For your problem, it would seem that the igniter/flame detector in the furnace is not functioning as it should. (This part does the both jobs.) You may have to remove the furnace to do much but I would check the wiring between the detector itself and the wire connection. Trace the wire and remove the connection at the circuit board and clean it well, both the wire end and the connection on the board, and then reconnect. You may have to replace the igniter/detector if cleaning and correct placement fails.
Theory: To detect the flame the igniter/detector has to sit in the flame. In the ignite mode, the igniter will flash 3 times and ignites the gas. When the flame ignites, the detector portion generates a very small voltage that is picked up by the circuit board during that 5 second period. If the flame is not detected then the furnace (or any other gas fired appliance) will shut down as a safety precaution. Since the voltage is very small, any corrosion etc. can prevent this happening.
You should find this article from the library helpful...
http://www.rvforum.net/joomla/index.php/16-rv-how-tos/333-furnace-troubleshooting
The fridge, the water heater, and the furnace all function similarly when operated on gas (propane).
Jkoht
Well-known member
- Joined
- Jul 24, 2017
- Posts
- 275
Check your thermocouple.
John From Detroit
Well-known member
There is a trouble shooting chart in our library. may even be two (I wrote one but I think Gary's (nearly identical) is in the library)
IF it lights this elminates most of the list so I'll give you the short form
The thermocouple.. a metal rod that sticks out in front of the burner.. Mine tested good (I can bench test it)
Now there are two different ignition systems. one is called "Single wire" in this system the thermocouple is also the "Center pin" of the "Spark Plug" THe other is multi-wire. Where the thermocouple and spark wires are ...different.
Spark voltage is roughly 1000 AC
THermocouple output 0.480 DC
A switch on the mother board (Control board) switches the flame sensor out during ignition phase
Imagine what happens to that senesitive (About 1/2 volt) Chip when it gets hit by 1,414 volts from the ignigation coil should the switch "hang" (it is a solid state switch by the way)
Pop goes the sensor
I finally decided to try a new DINOSAUR board.. Very well built. Kind of impressive actually and... Lo and behold.. There is a nifty little gas discharge tube on the Dino board that was not on the OEM. Now I'm guessing since I've not traced the circuit but it is in the perfect location to PROTECT that flame sensor chip.. Should the switch device not cut out in time and hit it with a kilovolt. the Discharge tube will flash and clip the voltage to something less than 100 (not sure the trigger point but 90 is a common for those tubes No reason they can not be made to trip lower).
IF it lights this elminates most of the list so I'll give you the short form
The thermocouple.. a metal rod that sticks out in front of the burner.. Mine tested good (I can bench test it)
Now there are two different ignition systems. one is called "Single wire" in this system the thermocouple is also the "Center pin" of the "Spark Plug" THe other is multi-wire. Where the thermocouple and spark wires are ...different.
Spark voltage is roughly 1000 AC
THermocouple output 0.480 DC
A switch on the mother board (Control board) switches the flame sensor out during ignition phase
Imagine what happens to that senesitive (About 1/2 volt) Chip when it gets hit by 1,414 volts from the ignigation coil should the switch "hang" (it is a solid state switch by the way)
Pop goes the sensor
I finally decided to try a new DINOSAUR board.. Very well built. Kind of impressive actually and... Lo and behold.. There is a nifty little gas discharge tube on the Dino board that was not on the OEM. Now I'm guessing since I've not traced the circuit but it is in the perfect location to PROTECT that flame sensor chip.. Should the switch device not cut out in time and hit it with a kilovolt. the Discharge tube will flash and clip the voltage to something less than 100 (not sure the trigger point but 90 is a common for those tubes No reason they can not be made to trip lower).
