Entegra Cornerstone – Furnace Igniter & Control Board Replacement

There is no worse feeling in full-time RV life than a critical system failing in the middle of January with nowhere to be towed and no mobile tech available until Monday. I’ve been there. That experience is why I now maintain everything on a schedule and know how to handle the repairs myself. On the Entegra Cornerstone, the furnace is one of those systems you absolutely cannot afford to ignore — when the igniter or control board fails, you lose heat entirely, and in cold weather that’s not just an inconvenience, it’s a safety issue. The good news is that both components are serviceable by a careful, methodical DIYer, and this guide walks you through exactly what I did to diagnose the failure, source the right parts, and get the furnace firing reliably again.

The Suburban Core That Actually Restores Heat to a Dead Cornerstone

When the igniter fails on a Suburban SF-35 or SF-42, you’re often looking at a complete furnace core replacement—the igniter alone won’t reignite, and the control board won’t cycle without it. This replacement core is the OEM-equivalent fix that gets you from no heat to full BTU output without guessing whether a patch repair will hold through the next cold snap.

What works

• Direct fit for SF-35, SF-35Q, SF-42, and SF-42Q—no adapter hunting or cross-reference confusion on a Cornerstone.
• Igniter and electrode come pre-assembled and tested, so you’re not troubleshooting two separate failure points after installation.
• Once seated, the furnace cycles cleanly and holds flame without the intermittent ignition tries that signal a failing core.

What doesn’t

• Shipping takes 5–7 days even with Prime; in January with no heat, that’s a long wait if your furnace dies on a Thursday night.
• Installation requires dropping the furnace shroud and disconnecting the propane line—a mobile tech can do it in under an hour, but if you’re new to the rig, budget 2–3 hours and have a second set of hands.

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.

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