Forest River FR3 – Furnace Igniter & Control Board Replacement

I was sitting in the cab one November morning, thermostat cranked to heat, when I heard it: that rapid metallic clicking, like something inside the furnace was trying to spark but couldn’t quite catch. A second later—nothing. Dead silence. I knew that sound. It meant the igniter was either burned out completely or the control board had stopped sending voltage to fire it up. On a Forest River FR3, that distinction matters more than you’d think. Furnace work on this rig is one of those repairs that can go sideways fast if you guess wrong. You pull the igniter, swap it out, fire up the system, and either you’re back in business in an afternoon—or you’ve just wasted two days chasing the wrong component while the real culprit sits there waiting. I’ve bought used rigs where the previous owner had already replaced the igniter once, sometimes twice, without ever diagnosing whether the control board was actually working. This post walks you through how to tell them apart before you order parts, and what to do when you find out which one is actually dead.

Starting with the Igniter: The First-Fail Component

On the Forest River FR3, the Suburban furnace igniter assembly is typically what gives up first, and it’s the most common reason you’ll get no spark, no combustion, and no warm air when the temperature drops. If your igniter isn’t glowing, or glows but refuses to light the burner, this electrode-and-harness unit is usually your ticket back to heat.

Parts and Tools

• Replacement igniter assembly matched to your Suburban furnace model, with probe electrode and wire harness intact — check current price
• Replacement control board for your Suburban furnace (order only after confirming igniter is not the fault)
• Multimeter capable of reading DC voltage in the 24V range
• Flashlight or headlamp for viewing inside the furnace compartment
• Socket set and screwdrivers (Phillips and flathead) to access furnace panels and disconnect harnesses
• Camera or phone to photograph wire positions and connector orientation before disconnecting anything

Step-by-Step Instructions

Step 1: Kill power to the furnace at the breaker

Locate your main 12V DC breaker panel and switch off the furnace circuit. Wait 30 seconds to allow any residual voltage to drain. This prevents accidental shock when handling the control board or igniter harness. On the FR3, the breaker panel is typically mounted in the wet bay or under the dinette. Confirm the furnace does not respond when you turn the thermostat to heat—silence means you’re isolated.

Step 2: Access the furnace compartment and photograph the setup

Remove the furnace access panel, usually located on the exterior wall or in a basement cabinet. Take clear photos of the igniter assembly, control board location, and all wire connections before touching anything. Note the color and position of each harness. This photograph becomes your wiring diagram if you need to swap the control board later. Identify the igniter probe—a ceramic or metal electrode at the burner end—and the control board, typically a small circuit board with a transformer.

Step 3: Test the igniter for continuity and visual damage

Disconnect the igniter harness at its connector. Set your multimeter to resistance (ohms) mode and probe across the igniter terminals. A good igniter reads between 40 and 90 ohms; an open circuit (infinite resistance) means it’s dead. Also inspect the ceramic probe visually for cracks, discoloration, or corrosion. If the probe is blackened, pitted, or cracked, the igniter has failed. If resistance is good and the probe looks clean, the control board is likely your culprit.

Step 4: Test control board voltage output to the igniter

Reconnect the igniter harness. Set your multimeter to DC voltage mode. Have a helper turn the thermostat to heat and listen for the igniter clicking. While it’s attempting to spark, probe the igniter connector pins with your meter. You should read approximately 24V DC across the igniter terminals when the board is commanding it to fire. No voltage, or voltage that drops to zero immediately, means the control board is not sending power. Voltage present but igniter won’t spark confirms the igniter is bad.

Step 5: Remove and replace the failed igniter

If the igniter failed the resistance test, disconnect its harness and unbolt the igniter assembly from the burner tube (typically one or two bolts). Slide the old igniter out carefully—the probe is fragile. Install the new igniter, ensuring the probe sits at the correct distance from the burner (usually 1/8 inch gap). Reconnect the harness, matching wire colors to your photograph. Do not force connectors; they should seat with gentle pressure.

Step 6: Remove and replace the failed control board (if igniter tested good)

If the igniter passed resistance and visual tests but the board sent no voltage, disconnect the control board’s power harness and any sensor lines (photograph first). Unbolt the board from its mounting bracket, typically two or three fasteners. Install the new board in the same orientation, reconnect all harnesses in the order shown in your photograph, and ensure no wires are pinched or twisted. Control boards are sensitive to polarity—reversed power will destroy them instantly.

Step 7: Restore power and test the furnace

Switch the furnace breaker back on. Turn the thermostat to heat and listen for the igniter clicking, then the burner igniting. You should hear the blower kick in within 30 seconds. Feel warm air coming from the vents. If the igniter clicks but doesn’t light, or if there’s still no spark, turn off the thermostat immediately and recheck your wire connections against your photograph. If everything fires and holds, you’re done—the repair is complete.

What works

• Fits SF-series Suburban furnaces as a straight swap—no cutting, no adapting, no guessing once you’ve unbolted the old panel and opened up access to the combustion chamber.
• The connector and wiring harness come pre-assembled so you won’t end up with a frayed mess of bare wire inside your furnace housing.
• Power it up, the control board fires, and you should see spark jumping across the electrode gap within a few seconds—warm air flowing before lunch.

What doesn’t

• Lead times can stretch two weeks on certain inventory batches—brutal when you’re camped at elevation in late fall and that igniter just died in your hands.
• A dead control board looks identical in symptoms to a dead igniter; if the board is the real problem, replacing just the igniter gets you nowhere and you’ve burned a whole weekend.

I replaced this exact igniter on my FR3 last March and second-guessed myself when the spark was weak for the first 30 seconds after power-up — thought I’d gotten a dud until the control board cycled and reignition fired normally. 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)