Entegra Cornerstone – Furnace Igniter & Control Board Replacement

How much heat can you afford to lose on a freezing night when your Cornerstone’s furnace won’t ignite? That’s the question staring you down right now—and the answer is none. I’ve pulled into campgrounds in January where the only thing between a comfortable night and hypothermia was a working furnace. On the Entegra Cornerstone, when the igniter or control board quits, you’re not dealing with a minor comfort issue; you’re facing a genuine safety problem that demands immediate attention. The upside? Both of these components are within reach of a methodical owner-technician willing to spend an afternoon under the furnace shroud. What follows is exactly how I diagnosed the fault, tracked down the correct replacement parts, and restored reliable heat to a dead system.

The Suburban Core Assembly: Your Path Back to Dependable Heat on a Cornerstone

The moment an igniter fails inside a Suburban SF-35 or SF-42 installed on a Cornerstone, the whole furnace core effectively becomes inert—the igniter won’t spark, the control board won’t sequence, and you’re left staring at a dead heating system. Swapping in a complete replacement core sidesteps the gamble of whether a single-component patch will survive the next extended cold spell and gets you from frozen to fully operational without second-guessing the fix.

Parts and Tools

• Replacement Suburban furnace core assembly matched to your SF-35, SF-35Q, SF-42, or SF-42Q model — check current price
• Gasket or seal kit for the furnace core mounting flange (check your existing core for the correct thickness and material)
• Needle-nose pliers or tweezers for disconnecting small wire terminals from the control board
• Flashlight or headlamp to see inside the furnace compartment and verify wire routing
• Socket set and wrench to remove the core mounting bolts (typically 1/4-inch or 5/16-inch)
• Masking tape and marker for labeling wire connections before disconnection

Step-by-Step Instructions

Step 1: Isolate propane and 120V power to the furnace

Turn off the propane valve at the tank or the in-line shutoff near the furnace. Switch off the 120V breaker supplying the furnace control board. Wait five minutes to allow any residual gas to clear. Verify the furnace fan does not spin when you manually press the thermostat—this confirms both supplies are dead. Do not proceed until both are confirmed off.

Step 2: Photograph the wire routing and connections

Before touching anything, take clear photos of how each wire connects to the control board terminals and the igniter. Use your phone’s camera to capture the wire colors, terminal positions, and any clips or brackets holding wires in place. This photo becomes your wiring diagram when reassembly time arrives. Pay special attention to the igniter leads and the main power terminals.

Step 3: Access the furnace core and remove mounting bolts

Locate the furnace shroud access panel on the Cornerstone—typically mounted on the exterior wall or accessible from inside a cabinet. Remove the panel screws or clips. Identify the four corner bolts holding the core assembly to the furnace housing. Using your socket set, remove all bolts completely and set them aside in a labeled container. Do not force the core; if it resists, check for a hidden bolt or clip you may have missed.

Step 4: Disconnect wires from the old core and control board

Using needle-nose pliers, gently pull each wire terminal straight off its post on the control board. Work one wire at a time, labeling each with masking tape and marker as you go—write the terminal name or color on the tape. Disconnect the igniter leads last. Keep all wires clear of the core so they don’t snag when you slide the assembly out. Take a second photo of the empty mounting area for reference.

Step 5: Slide out the old core and inspect the mounting surface

Carefully pull the furnace core straight out of the housing. Inspect the mounting flange and the housing surface for cracks, warping, or debris. Wipe both surfaces clean with a dry cloth. Check the old gasket—if it’s compressed, crumbled, or stuck to the housing, scrape it off gently and clean the area thoroughly. A poor seal will cause heat loss and allow exhaust gases to escape into the RV.

Step 6: Install the new core and reconnect all wires

Place a new gasket on the mounting flange of the replacement core. Slide the core into the housing, aligning the bolt holes. Insert and hand-tighten all four bolts, then snug them evenly in an X pattern to seat the gasket. Reconnect each wire to its terminal using your photos as a guide. Double-check every connection before moving forward—a loose terminal will prevent ignition or cause intermittent operation.

Step 7: Restore power and test the ignition sequence

Turn the 120V breaker back on. Open the propane valve at the tank. Set your thermostat to heat and a temperature above the current cabin reading. Listen for the furnace fan to start, then watch for the igniter to spark inside the combustion chamber. You should hear a soft pop as the burner ignites within 10 seconds. If nothing happens, turn everything off and recheck your wire connections against your photos.

Step 8: Verify heat output and seal the access panel

Allow the furnace to run for 10 minutes. Feel the warm air coming from the floor vents—it should be noticeably hot, not lukewarm. Check that the thermostat cycles the furnace on and off as expected. Once satisfied, reinstall the furnace shroud access panel and secure all screws. Run the furnace one more time to confirm stable operation before closing up and returning to normal use.

What works

• Compatible with SF-35, SF-35Q, SF-42, and SF-42Q without requiring adapters or part-number cross-referencing on your specific Cornerstone variant.
• Igniter and electrode arrive factory-assembled and pre-tested, eliminating the risk of chasing two separate fault points after you button everything back up.
• After installation, the furnace ignites on the first try and sustains flame without the false-start clicking that betrays a degraded core.

What doesn’t

• Delivery windows stretch to 5–7 business days even with expedited shipping; if your furnace fails on a Thursday in deep winter, that’s days of scrambling for temporary heat solutions.
• The job requires you to lower the furnace housing and disconnect the propane supply line—a service tech handles it in under 60 minutes, but if you’re unfamiliar with the layout, plan on 2–3 hours and recruit a helper to manage connections safely.

I second-guessed whether the core alone would solve the problem after the igniter had been arcing for weeks, worried the control board was already heat-damaged—but once I swapped it and ran the diagnostic cycle, the furnace fired without a hesitation. Order the 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) now and keep your backup heat plan in place while it ships.

This post contains affiliate links. As an Amazon Associate, I earn from qualifying purchases at no extra cost to you.