RV Repair: Suburban Furnace Maintenance, flame sensor, furnace maintenance

Question
Darren,

I have a thee year old Suburban RV furnace, Model NT-34SP, 34,000 BTU.  During our last camping trip it stopped hot air output.  The furnace lights and immediately extinguished itself, clears the combustion chamber and lights again, only to extinguish itself.  I replaced the gas tanks with freshly filled (30 lb) and still do not get any hot air.  I installed it myself three summers ago and it worked very well the last two winters.  This weekend, it was cold enough to use but it would not stay ignited.  When I remove the access panel and manipulate the thermostat, I see through the observation port on the left combustion chamber that the furnace lights and then goes out immediately.  The flame is a bright blue and appears to travel only 3/4 of the way down the row of gas ports before it extinguishes itself.  There is a removable plate on a box to the right side of the combustion chamber but when the two screws are removed the plate, connected to something, will not come out or rotate.  I believe there are wires there and I don't want to force anything, so I buttoned it back up.  The blower works well and the thermostat also functions properly.  

Can you tell me what I can do to service this unit and get it back on line with hot air.

Thanks,

Hans  

Answer
Hans,
    This should get you fixed up.

D. Burner Ignites But Shuts Off:
1. Check to be certain that flame sensor is over slots in the main burner and that the
main burner flame is burning against the tip of the flame sensor - adjust by bending
the sensor probe. NOTE: Sensor probe should be in the inner blue cone of the
burner flame, approximately 1/4" to 5/16" above the burner.
2. If the burner still goes off and into lockout, check the wire connections at the flame
sensor and the module board.
3. If wire connections are okay, check for continuity through the flame sensor wire.
4. If the continuity of the flame sensor wire is okay, check with microamp meter in
series with the flame sensor and flame sensor wire to be certain the flame sensor is
generating at least seven microamps within seven seconds after the burner is ignited.
Connect the meter as follows: (+) to sensor wire, (-) to sensor probe. Adjust the
position of the sensor probe, check air adjustment and check for carbon deposits on
the sensor probe if the reading is less than seven microamps.
5. When the flame sensor circuit is generating at least seven microamps, but the burner
still goes off and into lockout, replace the module board.

Good Luck and Happy Camping.

Darren