Issues with furnace staying on

If the probable fixes listed above don't solve it, you might have a gas regulator problem. It allows some gas to flow, but is right on the brink of delivering the right amount. A simple test would be to light all of the burners on the stove, and activate the heater. If you see the flames on the stove shrink substantially when the heater kicks on or when it goes out, I'd suspect the gas regulator.

Before replacing parts.........clean it

Everything is working. T-stat calls for heat, fan comes on, igniter is sparking/gas valve opening (which means sail switch...limit switch are good) main flame lights---goes out igniter relights.

What is not happening is control board seeing 'main flame on'

That usually means spark electrode is dirty, out of position or main flame is weak

Clean up the spark electrode with some emery cloth
Insure that spark electrode is centered and engulfed in main flame (spark electrode is fixed when installed but probe can be bent for positioning)
Main flame must be strong, steady blue flame with just tingles of yellow at tip (remove & clean orifice with alcohol) and check that you have 11" WC of gas pressure at furnace with other gas appliances in service (as suggested light off stove top burners on high, fire off WH then furnace and watch flames on stove top----they should slightly diminish then recover as furnace lights off. IF they diminish and remain smaller------regulator needs adjusted OR replaced)

only thing I would add is...
If the furnace always worked fine until you filled the propane tank...
I'd look at the propane tank / regulator, not the furnace.

JimM68 wrote:
only thing I would add is...
If the furnace always worked fine until you filled the propane tank...
I'd look at the propane tank / regulator, not the furnace.

I agree...check out what was last worked on before it failed.

Is the gas valve turned all the way on? Has to be all the way open.

if it runs for a few minutes and builds up heat before cutting out, it may be a disc thermostat/limit switch on the heat exchanger going bad.
service guide See page 24
Also you can try unplugging and reconecting all connections as oxidation can cause a voltage drop.

Sounds like you need one of these.. http://www.amazon.com/JCJ-M-500-furnace-Outside-Fitting/dp/B00076WQC2/ref=sr_1_2?ie=UTF8&qid=1387165281&sr=8-2&keywords=atwood+furnace+screen

When talking about cleaning, make sure the boiler its self is clean. I don't know about Atwood, but Suburban uses a cast iron burner. Because of the water in propane, the burner tends to rust. If you can pull the burner out, make sure the slots are clean, so they can flow fuel. In the Suburban, the slots will get completely clogged with rust.

katysdad wrote:

Also you can try unplugging and reconecting all connections as oxidation can cause a voltage drop.

I really appreciate everyone's help and wanted to get back to y'all with the solution. First off, the unite I have is not very friendly with making adjustments. I pulled the whole unit out and found the ignition, but trying to get that sucker out requires some serious disassemble. Since all was working before, I took the advice of katysdad & just pulled all connectors, made sure they were clean and had a good bite when back together. Replaced the unit and running like a champ now!!!!:B.
This unit really has no adjustments as everything seems to be sealed. I couldn't even locate the sail switch.
Anyway, thanks again. You where all a great help!!!!

Thanks for posting the result. You may well have helped someone else with the same or similar problem.