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Furnace problem

I have one furnace in my 36', mounted just above the bay with the lift up door. When the door is lifted the furnace shuts off because the door blocks the exhaust. The furnace started acting freaky a few weeks back, comes on the the burner lights, then goes off, does that three times, then shuts down. The code says it isn't seeing ignition, so I pulled the board, took it to my local RV shop with  a tester, they charged .5hrs ($60, new board on the internet was less than $100) said the board was ok. Put the board back, still shutting down. Later, got something out of the bay, slammed the door, the furnace started, worked fine till today. Same issue, tried the door, no change. I detect no voltage on the door micro switch, ,,should there be on one side ?
Dave W. (AKA Toyman )
'03, 270, 36', Build 6095, Pulling whatever I hook it to.

"Don't cry because it's over. Smile because it happened."
Dr Seuss

Re: Furnace problem

Reply #1 –
Sounds like the micro sw might be getting wiggie. I haven't checked but I would imagine it is in the ground circuit. I have bent mine a time or two and had it do that.
Bruce, Linda, and Macy
Zoey RIP 1/20/19
1999 U295 40' build #5400
2017 silver Jeep Wrangler, 1260 watts of solar on top
Moving around the country

Re: Furnace problem

Reply #2 –
Must be a normally open switch... just put a jumper across the switch until you can get a new one (assuming it is faulty and not just maladjusted in relationship to the closed hatch) and the furnace should stay on. Just make sure that you don't leave the hatch open while the furnace is running or even set to come on with the thermostat.
Don
The selected media item is not currently available.
Don & Tys
1999 U270 3602 WTFE #5402
Xtreme Stage 1 w/Headlight, Step Conversion, etc.
2009 Honda Fit Sport with Navi
Freedom is NOT "just another word for nothing left to lose"... with apologies to Kris Kristofferson

Re: Furnace problem

Reply #3 –
My guess is there's something else amiss, other than the door safety switch, as I would think any of the safety switches would close the gas valve and halt ignition attempts. Check to see if the flame proving device or thermocouple is loose, or dirty. Three strikes and your out is pretty common on burners, and they typically have a timer of 15 minutes or so to allow unignighted vapors to vent. If it has draft inducer fan they a diaphragm pressure switch that is a common failure point.
Old Phart Phred, EIEIO
89 GV ored 36' #3405 300 hp cat 3208 ATAAC side radiator, mountain tamer exhaust brake

Re: Furnace problem

Reply #4 –
I  would think a door switch would lock out any startup.
Sequence of operation is
signal from t stat sends power to board
Draft inducer fan starts and runs closing sail switch, this tells board you have draft.
Board starts igniter, clicking sound gas valve opens if no flame is sensed by thermocouple gas shuts off.draft fan runs system will try a nd light 3 times then lock out.
Early boards locked out after 1 try. Dinasour boards give you 3 trys.
91 GV U300 Unihome 40' Build 3811
6V92TA Detroit

Re: Furnace problem

Reply #5 –
Sounds like the igniter wire is bad.
The selected media item is not currently available.Bill&Doris 97 U270 36'
University of Parris Island Class of 66
Semper Fi  Build# 5174 MC#17094

Re: Furnace problem

Reply #6 –
The furnace is igniting, no doubt about that, it does it 3 times, just as the troubleshooting outlines for the factory furnace (board). I'm focused on the microswitch, or its wiring, because of that one past incident.
Dave W. (AKA Toyman )
'03, 270, 36', Build 6095, Pulling whatever I hook it to.

"Don't cry because it's over. Smile because it happened."
Dr Seuss

Re: Furnace problem

Reply #7 –
Can you get to the connections for the sail sw? By pass it to test the furnace.
I'm not sure if it would lite if the sail sw was the problem or if it would shut down the furnace after ignition.
John Duld
1995 U320C SE 40'

Re: Furnace problem

Reply #8 –
Quote from: Old phart phred –
Check to see if the flame proving device or thermocouple is loose, or dirty.
If sail switch does not close (indicating adequate air flow) then furnace will not attempt ignition.  Problem is elsewhere.

The door micro switch probably just completes a ground circuit when closed - hence, no voltage on either contact.

I think Old phart phred is on the right track.  It lights, but doesn't stay lit.  Bad thermocouple?
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Furnace problem

Reply #9 –
If the burner is lighting but then shutting down you have a problem with the flame sensor .flame has to be sensed in order for control board to keep gas valve energized.clean sensor tip with emory cloth or something snd wiggle clean wire end terminals
91 GV U300 Unihome 40' Build 3811
6V92TA Detroit

Re: Furnace problem

Reply #10 –
There are two different setups for sensing the flame.  Depending on furnace model, thermocouple may be built into the ignitor (local sense), or it may be a separate piece (remote sense).  See diagrams in manual linked below:

http://bryantrv.com/docs2/docs/hflamefurn04.pdf
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Furnace problem

Reply #11 –
Quote from: stump –
If the burner is lighting but then shutting down you have a problem with the flame sensor .flame has to be sensed in order for control board to keep gas valve energized.clean sensor tip with emory cloth or something snd wiggle clean wire end terminals

This.

Step 1, rule out micrositch cicuit by jumping it.

step 2 check flame sense circuit (find a manual).

Remember, it used to work and stopped....can't be too complicated.
1998 U270 34'

Re: Furnace problem

Reply #12 –
The thermostat calls for heat,the blower comes on, sail switch closes, ingniter comes on,gas valve opens, gas ignites, igniter and it's wire become the flame sensor to the board to let it know that all is working, if you have no flame it will shut down, if you have a flame
 and it shuts down it could be a bad igniter or a bad igniter wire.
The selected media item is not currently available.Bill&Doris 97 U270 36'
University of Parris Island Class of 66
Semper Fi  Build# 5174 MC#17094

Re: Furnace problem

Reply #13 –
To cold to mess with it today, leaving on a cruise in the morning. Think I'll wait till it warms up....then I won't need it !!
Dave W. (AKA Toyman )
'03, 270, 36', Build 6095, Pulling whatever I hook it to.

"Don't cry because it's over. Smile because it happened."
Dr Seuss

Re: Furnace problem

Reply #14 –
Hope this helps: I've been having problems with my rear Hydro Flame (Attwood) furnace for a while: it would fire, then not, on and on. My VOM got a huge workout, everything seemed to be getting juice. Cleaned the terminals, no help. O.K. new board time. Had a new Dinosaur board, a "Universal" spare for the front Attwood, installed it, same deal. Went to the dark side and figured it was the igniter. Now, I've had furnaces for thirty years and it was almost ALWAYS the board, so something just did not make sense. Before pulling the furnace, I called Dinosaur and explained the problem, giving them the model # & year of the furnace. They checked, and sent me another board, which I installed just now. Fan came on, red light on the board, heard igniter "click" once and, BINGO, green light and heat!  Moral? Make sure Dinosaur (who I like) knows what you're installing it in!  ^.^d  Fingers crossed.
1993 U-240 "La Villa Grande"..CAT 3116 w/ Pacbrake PRXB...Allison 3060 6-speed..
Previous: 1983 Airstream 310 turbo diesel, 1979 Airstream 280 turbo diesel
                                      Build # 4297
                                      PNW natives
                      Home base:  'Cactus Hug' (Ajo, Arizona)
                        DW Judy & Chet the wonder dog
                        Full-Timers 'Sailing the asphalt sea'

Re: Furnace problem

Reply #15 –
Ditto here. New Dino board, intermittent ignition gone.
1997 U270 34FT Build 5140 Cummins 8.3 Allison 3060R
Solar 1920Watts, 14KWH lithium. Orion BMS.