Help! Furnace Won’t Latch-In

[gazunni]

Hello All

I have a 2003 Holiday Rambler Vacationer

Today I tried lighting the furnace and it won’t latch in.

There is enough propane and the house batteries have enough voltage. I also tried it with the generator running.

When I turn the thermostat system switch, the furnace fan engages, you can hear the light up sequence rumble then it shuts down. It attempts the sequence 3 times then locks-out as it is designed to do.
The system can only be unlocked by cycling the system on/off switch.
I attempted the sequence a total of 4 times, each time the system attempted lighting 3 times but it simply won’t latch-in.

Any ideas, other than take to the dealer?

The LPG tank levels show 2/3 full on the inside panel and the gauge on the tank shows just under 1/2 so there should be more than enough propane.

Thanks for your constructive ideas.

[Bob_C]

How long since an air hose was taken to the exhaust vent?

[SteveJ.]

Originally Posted by gazunni

Hello All

I have a 2003 Holiday Rambler Vacationer

Today I tried lighting the furnace and it won’t latch in.

There is enough propane and the house batteries have enough voltage. I also tried it with the generator running.

When I turn the thermostat system switch, the furnace fan engages, you can hear the light up sequence rumble then it shuts down. It attempts the sequence 3 times then locks-out as it is designed to do.
The system can only be unlocked by cycling the system on/off switch.
I attempted the sequence a total of 4 times, each time the system attempted lighting 3 times but it simply won’t latch-in.

Any ideas, other than take to the dealer?

The LPG tank levels show 2/3 full on the inside panel and the gauge on the tank shows just under 1/2 so there should be more than enough propane.

Thanks for your constructive ideas.

Stating the size and make and for bonus points, the model number would be a good thing so folks can know what you have.


Wiring to the the gas valve from circuit board or the board itself come to mind as well as "crap" in the burner or self destructed or rusted burner.

[Doug.terri5]

Gazunni, if your Coach has been stored, are you sure the propane is on? Also, have you turned some stove burners on to bleed any air from the system?

I know these are simple solutions but sometimes that’s all it is.

Best to you!

[Pillbox]

Do you hear the ignitor trying to light?
If yes, its your burner, or ignitor, or both, but can also be the ignitor clearance to the burner.

[Arch Hoagland]

Will your stove top burners light?

Will your water heater work on gas?

[gazunni]

[ATTACH][ATTACH][/ATTACH][/ATTACH]

Hello All.

Some additional information
1. I had the propane tank filled up just to ensure
2. The gas stove top lights up with no issues.
3. Took the side panel off and took pictures...attached
4. Reset and turned on switch on thermostat.
Very clearly you can hear the igniter sparking and there is the woof as the main burner lights. The exhaust gas immediately gets hot and the fan is running with no issues.
5. About 10 seconds after light, the main burner shuts down and the fan shortly after.
6. This repeats 3 times then locks out.
7. There is a red flashing light on the control
board.

Any thought. Still seems to me like the flame proving sensor is not working/sensing. I cant actually see where the sensor is or if it is aligned in the combustion chamber.

Any thoughts or help is appreciated.

[oldnavycdr]

I had this very issue with my Atwood furnace -- 3 attempts and then lockout. The flame detector is not sensing flame (or sending the signal to the igniter board). On mine the igniter & flame sensor are a combined part. It is kind of a pain to replace but there are several YouTube videos on this explaining how to replace. While I was at it I replaced the burner head and igniter board as well. I discovered that my original burner head was just fine -- no rust or burn through so I have a spare. Before you replace make sure your grounds are good.

[oldnavycdr]

Also, the flashing LED is giving you a fault code. The codes are listed on the top left label in the picture you posted. 2 flashes = "Flame Sense" fault.

[shootist]

The high limit switch or the flame sensor would be the two non board items that could cause it. The sail switch , thermostat and the main switch which is a breaker on some models and the high limit are on the 12v proving side. The flame sensor is on the board side by itself as far as circuitry.

[castelek]

Had same problem with 2005 HR Ambassador. Ended up being a bad igniter/ sensor. Not easy to change but can be done without removing heater from coach.

[gazunni]

Update

I took the furnace apart. When I pulled it some pieces of a hardened hornets nest came out.
Looked at the burner and igniter and both were in good condition except the connection on the igniter. The terminal and connector were corroded. Replaced the connector and cleaned up the terminal.
Put it all back together. And the SAME problem still occurred. After about the 5th attempt it finally latched in. Tried on and off several times and it continued to work. Next day, same problem.
Got a new igniter board and replaced same. It only took 5 minutes to remove the old and install the new one. Everything worked first time.
I expect the flame sensor module is intermittently faulty.

Hopefully by posting my journey it may help others.

Thanks for all the feedback and advice.

[Old-Biscuit]

Originally Posted by gazunni

Update

I took the furnace apart. When I pulled it some pieces of a hardened hornets nest came out.
Looked at the burner and igniter and both were in good condition except the connection on the igniter. The terminal and connector were corroded. Replaced the connector and cleaned up the terminal.
Put it all back together. And the SAME problem still occurred. After about the 5th attempt it finally latched in. Tried on and off several times and it continued to work. Next day, same problem.
Got a new igniter board and replaced same. It only took 5 minutes to remove the old and install the new one. Everything worked first time.
I expect the flame sensor module is intermittently faulty.

Hopefully by posting my journey it may help others.

Thanks for all the feedback and advice.

Flame sensor (flame proving) is via the Spark Electrode
When flame ignites it generates an AC current in the flame. This current is rectirifed into a DC vurrent which circuit board senses via feedback thru spark electrode



Spark electrode is dual function
Provides high voltage spark for ignition via transformer on board and Orange wire
Provides feedback of millamp signal for flame proving..change in current is sensed by circuit board


Electrode must be clean (no soot/carbon)
Electrode wiring & connections must be clean/tight
Electrode ceramic can NOT have any cracks or wire be loos inside the ceramic
Ground (assembly mounting screw) must be clean/tight




4 wires on your circuit board
*White---12VDC coming from sail switch and high temp limit switch. Goes back to circuit board proving air flow is adequate----allows circuit board to send DC to gas valve/spark electrode
*Red---12VDC from circuit board to gas valve
*Blue---12VDC from thermostat to circuit board. Allows circuit board to send DC to FAN motor via blower circuit (which gets the DC via the power circuit from the On/Off CB)
*Yellow----Ground wire. Goes to terminal block with 12VDC Neg and motor ground