Condensing gas furnace

We have a condensing lp gas furnace (no name on the panel, but the manual says Johnson Controls) in our home as a back-up to our wood furnace, both are forced hot air with seperate ductwork. The furnace is suspended horizontaly hanging from the floor joists. Quite often when the gas furnace has not been in operation for several hours, ie: we don't get up at 3am to load the wood into the wood furnace, the gas will not fire when heat is called for.

Here's what happens, there are 4 "chambers" , the furnace starts up and the top 3 fire in the start up, but the lower one of the four doesn't. The furnace tries to ignite three times then blocks out for an hour and blows cold air. Most times if I feel the cold draft I awaken and shut off the power to the unit. An hour later I turn the power back on and it fires on all 4 "cylinders". If I hear the furncace try to start and get to it before it makes the 3rd try, I can shut the power to the unit, wait a couple of minutes, turn on the juice and then it will start.

I live in a rural area and we don't have a lot of service techs, the local tech has been over several times to check out the unit. By the time he gets there it been longer than the 1 hour block out time, and he checks things can't find out the problem. the trouble shooting lights tell what could be, but never what it is, all for the $100 service fee.

Have you any idea what it could be? The furnace is 3 years old, and it has done it every winter, and I am at wits end.