Community Forums

F4Jock · 04-26-2018, 04:33 PM

Furnace blower comes on but no flame MOST of the time but every once in a while it heats.

Any thoughts on where to begin troubleshooting?

Old-Biscuit · 04-26-2018, 04:45 PM

'Sail Switch'

It is just a micro switch with a 'paddle' stuck in airflow
If dirty.....paddle will not move or contacts do not make up

No Sail Switch....no DC to circuit board to allow for sparking/gas valve opening

winniman · 04-26-2018, 05:18 PM

My old coach did the same thing. The thermostat was worn out, and if I screwed around it long enough, I could get the furnace to come on. Otherwise, the fan would just come on, and thats all. I found if I slide the Off/Gas/elect. switch half way between off and gas, it would light the furnace. It would stay working until I turned it off, then I would have to screw with it again. I ordered a new thermostat, and never had the problem again. The coach was a 2000 winnebago 37g. It had the heat pump/ electric A/c, as well as a propane furnace. It had the three way thermostat. Propane furnace/Electric furnace/ air conditioning, all on one thermostat. You dont state what you have. Put your rv in your signature so people know what you have.

Bob_C · 04-26-2018, 05:35 PM

Light your stove and when try'n the furnace, watch the flame on the stove......gets yellow?.......regulator..

F4Jock · 04-27-2018, 04:49 AM

Thinking that it was the thermostat, an old 4 button Duo Therm Comfort Control, I went to eBay looking for an exact replacement. I found what I thought was one but it turned out it was a gentleman in Nebraska who fixed them. It was about $140 but I figured it would save me the hassle of messing with installing a 5 button so I went online and ordered it.

Much to my surprise I got a phone call about half an hour later from a gentleman named Jim who said that he actually refurbished them and didn't have new or remanufactured ones to sell. He proceeded to ask me about the symptoms of my unit and said "I think I know your problem, you have the thermostat confused between zones 1 and 2 and if you are commanding it to do something in zone 2 that isn't the same as in zone 1 then it will not do either." I went outside and reset both zones to do the same thing and it worked! Jim is refunding my money but keeping $30 at my insistence because of the time and effort he saved me. Besides, he is selling his knowledge as well. If anyone is having Duo Therm problems I suggest you look him up. frerichselectronics.

Old-Biscuit · 04-27-2018, 10:57 AM

Glad you found it was just operational error vs throwing parts at it

'Devil is in the details'

That info would have been helpful in first post.

F4Jock · 04-28-2018, 05:13 AM

Quote:

Originally Posted by Old-Biscuit

Glad you found it was just operational error vs throwing parts at it

'Devil is in the details'

That info would have been helpful in first post.

Thanks! Actually, I did not have all of that information when I first had the problem. I knew there were two control zones but thought they were either independent or essentially zeroed out when I switched away from them. I also did not know that selecting AC in Zone 2 would affect selecting heat in Zone 1 when you switched away from it even though Zone 2 has no selection for heat. All I knew was that, when called for, the heat came on only sometimes with no apparent reason. I did not in any way connect the possibility of Zone 2 interfering with Zone 1. Apparently Jim has seen this scenario before as he immediately suggested what might be wrong and the fix. He also gave me a factory reset procedure to use in case the thermostat / controller's brain had been totally scrambled.

If zones or other functions do not work - do this Reset Procedure for your 4 button Dometic thermostat.

Subject: reset procedure for Dometic 4 button thermostat

1 Connect the phone type cable to the back of the thermostat and turn on the power switch.
2 If possible, on any zone set the heat and cool (each) to 70 degrees on the display.
3 Momentarily depress and release the mode switch - the display lighting should come on.
4 Depress and together hold down the two bottom buttons (up and down).
5 While still holding the two bottom buttons add the third button from the bottom (mode button).
6 Release the third button (mode) first.
7 Then release the two bottom buttons (up and down) together.
8 Momentarily depress the mode button. The display light should go off. If not, repeat steps 1-8.

This reset procedure programs your thermostat to your RV's systems and temporarily defaults to settings of 68F for the heating and 72F for the cooling. Look for these temperatures as proof

Having purchased the RV used (Third Owner)I have no instruction manual for this particular system nor can I find one. It's people like Jim and those on this site, knowledgeable and willing to help, that have increased my knowledge base about the National we own. In any case I picked up another useful bit of information and found someone who can help people with the same thermostat without charging them an arm and a leg. Win / Win!

F4Jock · 04-28-2018, 04:25 PM

Quote:

Originally Posted by winniman

My old coach did the same thing. The thermostat was worn out, and if I screwed around it long enough, I could get the furnace to come on. Otherwise, the fan would just come on, and thats all. I found if I slide the Off/Gas/elect. switch half way between off and gas, it would light the furnace. It would stay working until I turned it off, then I would have to screw with it again. I ordered a new thermostat, and never had the problem again. The coach was a 2000 winnebago 37g. It had the heat pump/ electric A/c, as well as a propane furnace. It had the three way thermostat. Propane furnace/Electric furnace/ air conditioning, all on one thermostat. You dont state what you have. Put your rv in your signature so people know what you have.

Strangely enough my data IS in my signature. I'll have to see why it did not come through.