Most of the service calls I get aren’t emergencies — they’re deferred maintenance that finally gave up. The owner noticed something off weeks ago, ignored it, and now they’re calling me from a campground two states from home. Nine times out of ten, this repair could have been done for a fraction of the cost if they’d caught it early. With the Thor Chateau’s furnace igniter and control board, the warning signs are usually there — the furnace cycles on but never actually fires, you hear the blower kick in and then nothing, maybe a faint clicking that stops short of ignition — and what starts as a minor igniter failure can stress the control board to the point where you’re replacing both instead of one. I’ve written this guide the same way I’d walk a capable owner through the repair on-site: no fluff, no skipped steps, just what you actually need to get heat back in your rig before the temperature drops tonight.
Parts & Tools You’ll Need
- Suburban RP-35Q 35,000 BTU/h RV Replacement Core for Suburban Furnace Series SF-35, SF-35Q, SF-42, SF-42Q, and SF-Q (2609A) — Suburban/Atwood RV furnace (replacement unit)
- Fit For Suburban RV Furnace Parts 232286,Single Probe Gas Furnace Igniters Electrode with Wire Assembly, Camper Furnace For Suburban 232286 Above 934701426 SF-20, SF-25, SF-30, SF-35 (SF Series) — Furnace igniter electrode
- DTAIR 33082 Sail Switch Replacement for Select Dometic Atwood RV Furnace(Pack of 2) — Furnace sail switch
- 520814 Rv Water Heater Module Board Ignition Control Circuit Board Compatible with Suburban Furnace SW4D, SW6D, SW6DE, SW12D, SW6DEM RV Water Heaters,Replace 520814 520820 520871 33550L (With lid) — Furnace circuit board / control board
- DTAIR 33082 Sail Switch Replacement for Select Dometic Atwood RV Furnace(Pack of 2) — Furnace high-limit switch
- Suburban 232684 RV Furnace 12v SF-Series DC Blower Motor, SF-35, SF-35F, SVF-35, SF-42, SF-42F OEM Caliber — Furnace blower motor (12V DC)
- RV Carbon Monoxide & Propane Gas Alarm, Briidea Dual LP/CO Detector with Separate LED Indicator Light, 100dB Loud Alarm, 12 VDC, Black — Propane/CO combo detector alarm
- FKM Pro Digital Multimeter Tester TRMS 6000 Counts,Smart Rechargeable Voltmeter 5″Color LCD,Auto-Ranging Automotive Multimeters,for AC/DC Current/Voltage,NCV,Ohm,Capacitance,Resistance,Continuity,Temp — Digital multimeter
Step 1: Diagnose Furnace Failure and Prepare Work Area
Start by locating your Thor Chateau’s furnace compartment, typically found in the basement cabinet or utility area. Turn off propane at the tank and disconnect the 12V DC power from your RV’s battery, then visually inspect the furnace for any visible damage, corrosion, or loose connections around the igniter electrode and control board. Use your digital multimeter set to DC voltage to confirm zero power at the furnace terminals before proceeding—this critical safety step prevents electrical shock and accidental ignition.
Step 2: Remove Old Furnace Igniter Electrode Assembly
Locate the igniter electrode mounted near the burner assembly; it’s a ceramic-tipped metal rod approximately 2-3 inches long. Disconnect the spade connector terminal from the electrode and carefully unscrew the mounting bracket from the furnace housing using a 1/4-inch socket or wrench. Gently pull the electrode straight out to avoid cracking the ceramic tip, then set it aside for inspection to confirm ignition failure.
Step 3: Access and Remove the Furnace Circuit Board
Open the furnace access panel or control box cover, taking note of all wire connections to the circuit board—you may want to take a photo for reference during reinstallation. Carefully disconnect each spade connector and any press-fit terminals from the old control board, including connections from the sail switch, high-limit switch, blower motor, and propane valve. Unscrew the circuit board from its mounting clips (typically 2-3 screws) and remove it completely.
Step 4: Install the New Furnace Circuit Control Board
Position your new furnace circuit board onto the mounting clips and secure it with the original screws, ensuring it sits flat and flush against the housing. Reconnect all terminals to their original positions using your photo reference—verify that the sail switch, high-limit switch, and igniter connections are firmly seated and match the board’s terminal layout. Double-check that no wires are pinched between the board and housing, as this could cause shorts or fires.
Step 5: Install the New Furnace Igniter Electrode
Insert the new igniter electrode into the mounting bracket with the ceramic tip pointing toward the burner assembly, ensuring it’s positioned approximately 1/8 inch from the burner flame path (consult your Suburban/Atwood furnace manual for exact spacing). Tighten the mounting bracket securely but gently—avoid over-tightening, which can crack the ceramic. Reconnect the spade connector terminal firmly to the electrode, ensuring the connection is tight enough that it won’t wiggle by hand.
Step 6: Verify All Furnace Components and Seal Housing
Inspect the sail switch, high-limit switch, and blower motor connections one final time to confirm they’re secure and properly seated on the control board terminals. Check that the furnace access panel gasket is clean and undamaged, then reinstall the panel and tighten all fasteners evenly. Reconnect the 12V DC power to your RV battery and restore propane flow at the main tank valve.
Step 7: Test Furnace Ignition and Safety Systems
Set your RV thermostat to heat mode at a temperature above the current cabin temperature, then listen for the blower motor to engage and the furnace to cycle on—you should hear a distinct clicking sound as the igniter electrode sparks, followed by the burner lighting within 2-3 seconds. Allow the furnace to run for a full 5-minute cycle and confirm hot air is flowing from your vents; if ignition fails or the high-limit switch shuts down the furnace, stop immediately and recheck all electrode and board connections. Finally, test your Propane/CO combo detector alarm to ensure it functions properly and displays normal air quality readings.