Furnace problem

[Clarabelle]

I have a Suburban furnace in my PUP, model DD-17DSI, that doesn't heat as well as it did last April. The burner ignites as it should, but it doesn't seem to be putting out enough heat.
I've looked through the spy hole, and can see that the burner is burning blue at the base of the flame, but there is considerable yellow higher up in the flame. The manual says it should be all or mostly blue flame.

Does anyone know how to adjust the air/gas mixture to get a hotter flame? All the manual says is see an authorized technician.

[PattieAM]

Your burner assembly may be gunked up with bug nests and need to be blown out with compressed air (when furnace is off/gas is off).

[ScouterMom]

I'd check out the bugs too - hornets and mud wasps love camper furnace vents!

I would also check your propane connections - get a spraybottle with some water and regular dishsoap - spray it on all the connections and see if you have any leaks when the propane is turned on.  If it is leaking, you will get bubbles. Check any hoses or copper lines that are exposed, make sure you don't have any pinholes or wear on them.

Have you had any of the lines disconnected recently?  Sometimes you can get condensation in the lines if they are left open.  I don't remember how to dry them out, but if there are no leaks as above, It couldn't hurt to disconnect them, blow them out, and reconnect them.

If you have had the propane tanks filled, topped off or changed recently, you might have the tanks and valves checked out.