Complete repair guide for the Tiffin Open Road Allegro – Furnace Igniter & Control Board Replacement. Follow these steps to diagnose and fix the issue yourself.
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 Issues and Prepare Workspace
Begin by identifying whether your furnace is failing to ignite, producing weak flames, or not responding to the thermostat—these symptoms typically indicate either a faulty igniter electrode or a failed control board. Turn off the propane supply at the tank, disconnect the 12V DC power from your RV’s battery, and allow the furnace to cool for at least 30 minutes. Set up your workspace in the basement compartment with adequate lighting and lay out your digital multimeter, replacement parts, and a small container to organize fasteners during disassembly.
Step 2: Access and Remove the Furnace Unit
Locate your Suburban/Atwood RV furnace mounted in the basement compartment—it’s typically a rectangular metal box measuring approximately 24″ x 16″ x 12″. Disconnect the propane line by turning the shutoff valve and unthreading the compression fitting with two wrenches, then disconnect all electrical harnesses including the 12V power connector and any thermostat wiring. Unbolt the furnace from its mounting brackets using a 3/8″ socket wrench, noting the bracket positions, and carefully slide the unit out toward you—it typically weighs 15-20 lbs.
Step 3: Test and Replace the Igniter Electrode
Set your digital multimeter to the ohms setting and probe the furnace igniter electrode terminals to check for continuity—a healthy electrode reads 4-14 ohms, while an open circuit (infinity reading) indicates failure. Remove the igniter electrode by unthreading its mounting bolt from the burner assembly and disconnecting its ceramic insulator connector. Install the new furnace igniter electrode by reversing this process, ensuring the electrode tip sits approximately 1/8″ away from the burner port and the connector is fully seated.
Step 4: Inspect and Replace the Sail Switch
Locate the sail switch—a small paddle-shaped component mounted near the blower outlet that detects airflow before ignition occurs. Test it by gently moving the sail arm and listening for an audible click; if it’s stuck, corroded, or silent, replacement is necessary. Disconnect the sail switch harness, unbolt the switch from its bracket, and install the new furnace sail switch in the same orientation, ensuring the paddle can move freely without obstruction.
Step 5: Remove and Replace the Control Board
The furnace circuit board is typically mounted on the interior wall of the furnace housing with 2-3 screws; take a photo of all wire connections before disconnecting them to ensure accurate reassembly. Unbolt the old furnace circuit board and carefully remove it—note that it contains sensitive electronic components, so avoid touching the circuitry itself. Install the new furnace control board in the same location, reconnect all wires to their original terminals using your photo as reference, and ensure all connectors are fully seated and secure.
Step 6: Reinstall Furnace and Reconnect All Systems
Slide the furnace unit back into the basement compartment, align it with the original mounting brackets, and secure it with the bolts you removed—torque them to approximately 30-40 inch-pounds to avoid cracking the housing. Reconnect the propane supply line using two wrenches to tighten the compression fitting, then reconnect all electrical harnesses including the 12V battery power and thermostat wires, ensuring each connector clicks fully into place. Turn the propane supply valve back on at the tank and verify there are no gas leaks by applying soapy water to all fittings—bubbles indicate a leak requiring immediate attention.
Step 7: Test Furnace Operation and Verify Safety Systems
Reconnect your RV’s 12V battery power, set the thermostat to heat mode at 75°F, and listen for the blower motor to engage within 10 seconds followed by the igniter electrode clicking and the burner igniting within 30 seconds. After 5 minutes of operation, feel the warm air exiting the vents and confirm the propane/CO combo detector alarm is not sounding—any alarm indicates a serious safety issue requiring immediate furnace shutdown. Allow the furnace to run for 15 minutes, then verify the high-limit switch cuts power if the unit overheats, confirming all safety interlocks are functioning correctly before declaring the repair complete.