How to Troubleshoot an RV Furnace (Propane) That Won’t Ignite: Complete Heating Guide

When temps drop, a cold coach can end a trip fast. Learning how to troubleshoot an RV furnace (propane) that won’t ignite helps you restore safe, steady heat without guesswork. This step-by-step RV furnace troubleshooting guide covers thermostat checks, 12V power, airflow and the sail switch, LP gas supply, igniter/flame sensor issues, exhaust/combustion air paths, boards, and common error patterns—plus preventative maintenance so your heater fires the first time, every time. For expert diagnostics or parts, schedule service at Daisy RV.

Safety First: Carbon Monoxide & LP Gas

  • If you smell gas, shut cylinders off, ventilate, and stop troubleshooting until the leak is resolved.
  • Test CO and LP detectors and replace any beyond their service life.
  • Keep combustibles clear of furnace and ducts; never block return air.
    Need a certified LP pressure/leak check or detector replacement? Book with Daisy RV.

How an RV Furnace Works (Quick Map)

  1. Thermostat calls for heat → 2) Blower starts and purges → 3) Sail switch proves airflow → 4) Gas valve opens & igniter sparks → 5) Flame sensor proves flame → 6) Heat exchanger warms ducts → 7) Thermostat satisfies → 8) Cool-down blower cycle.
    If any “prove” step fails, the board locks out and the furnace won’t light.

Fast Triage: What Is Your Furnace Doing?

  • Blower never starts: power/thermostat problem.
  • Blower starts, no ignition clicks: airflow/sail switch not proving.
  • Clicks/sparks but no flame: gas supply, pressure, or igniter positioning.
  • Lights, then shuts off: flame sensor, ground, or airflow/overheat (limit switch).
  • Short cycles, lukewarm air: low voltage, restricted ducts, or thermostat setting.

Tools You’ll Want Handy

Multimeter (DC), #2 square/Phillips drivers, flashlight, compressed air, soft brush, vacuum, emery cloth, silicone-safe cleaner, spare fuses (ATC), butane lighter (for soot test), and new return/duct filters if your rig uses them.

Step 1: Thermostat & 12V Power Checks

  • Mode & Setpoint: Confirm HEAT mode and the set temperature above room temp.
  • Battery Voltage: Furnace needs healthy 12V. Check at the furnace leads with blower running; below ~11.0–11.5V can cause lockouts and weak ignition. Charge or diagnose batteries/converter if low.
  • Fuse & Connections: Inspect furnace fuse, spade connectors, and grounds for corrosion or looseness. Clean/tighten grounds to bare metal.

Step 2: Airflow & the Sail Switch (Most Missed)

The sail switch proves that the blower is moving enough air to safely ignite. Dust, pet hair, or blocked returns/ducts keep it from closing.

  • Return Air: Open the louvered grill; never block with rugs or bins.
  • Ducting: Verify at least one primary duct is fully open and not kinked/ crushed.
  • Filter Screens: Some installs add aftermarket screens; clean or remove if restrictive.
  • Sail Switch Cleaning: With power OFF and LP OFF, access the furnace, gently blow out dust on the blower wheel and sail switch arm; ensure the arm swings freely.

If the blower runs but you never hear the igniter click, the board likely isn’t seeing the sail switch close—restore airflow first.

Step 3: LP Gas Supply & Regulator Health

  • Cylinders On & Fuel Available: Crack valves slowly to avoid tripping the excess-flow device.
  • Other LP Appliances: Does the stove burn strong blue flame? If weak/yellow, suspect low LP or regulator issues.
  • Regulator Vent & Pigtails: Check for insect nests in the vent cap and cracked hoses. Replace aged pigtails.
  • Leak Check: Soapy water on fittings (no bubbles allowed). If in doubt, have a certified LP test performed at Daisy RV.

Step 4: Ignition—Gap, Ground, and Flame Sensor

  • Igniter Position: The spark probe should sit in the burner flame envelope per your model spec (often ~1/8–3/16″ gap to burner surface). Gently realign if bent.
  • Clean the Probe: Lightly scuff carbon with emery cloth; oil/soot insulates the sensor.
  • Ground Path: The flame sensor relies on microamps through ground. Clean the burner bracket ground and chassis ground to shiny metal.
  • Spark Present, No Flame: Verify gas valve gets 12V during spark; if it does, but no flame, check orifice for debris and burner tube for spider webs (very common). Clear carefully and vacuum.

Step 5: Flame Starts Then Quits (Proving & Overheat)

If burners light for 2–10 seconds then shut off:

  • Flame Sensor Signal Weak: Re-clean probe and grounds; ensure stable blue flame touching the sensor.
  • Limit Switch (Overheat): Restricted ducts, crushed hose, closed registers, or blocked return can overheat the heat exchanger and trip the limit; open airflow and reset.
  • Low Voltage Under Load: Measure DC at the furnace while igniting; sagging below threshold causes erratic flame proof.

Step 6: Exhaust & Combustion Air—Clear the Path

Birds, wasps, and mud daubers love furnace vents.

  • Exterior Intake/Exhaust: Remove screens and clean soot. Look inside with a flashlight for nests; clear gently.
  • Soot Trails at Vent: Indicates poor combustion—clean burner, verify regulator pressure, and ensure proper air shutter (if adjustable).

Step 7: Control Board and Wiring Harness

After airflow, gas, and ignition are correct, suspect the board/harness.

  • Visual Inspection: Burn marks, swollen components, or moisture exposure.
  • Harness Pins: Tight, corrosion-free pin fit; reseat connectors.
  • Diagnostics: Some boards flash codes; note patterns before cycling power.
  • Replacement: Use model-matched boards; verify polarity and standoffs to avoid shorts.

Step 8: Thermostat Wiring & Anticipator/Settings

  • Two-Wire Call for Heat: Confirm continuity when calling for heat.
  • Digital Stats: Check batteries (if used) and configure “FURNACE/ GAS” mode.
  • Anticipator/Settings: For legacy stats, improper anticipator causes short-cycling; set per furnace spec.

Common RV Furnace Troubleshooting Scenarios

  • RV furnace not igniting after refill: Open tank valve slowly; purge air by running stove for a minute; then retry furnace.
  • Runs on shore power but not boondocking: Batteries sagging; clean lugs, charge fully, consider heavier cabling or battery upgrade.
  • Heats for 5–10 minutes then quits: Overheat from blocked return/duct, or failing limit switch.
  • Blower runs constantly, never fires: Sail switch or low voltage; verify ducts/returns and 12V under load.

Preventative Maintenance for Reliable Heat

  • Pre-Season Service (Fall): Clean burner/orifice, blow out blower housing, verify duct flows, tighten grounds, and test run.
  • Quarterly: Vacuum returns, confirm detectors, crack the furnace monthly to keep parts moving.
  • Annually: LP system pressure/leak test, full furnace inspection, and CO/LP detector date check.
    Prefer a worry-free winterization and furnace tune? Schedule at Daisy RV.

When to Call a Pro Immediately

  • Repeated lockouts with strong gas and clean ignition path
  • Sooting at the vent, rumbling flame, or burner “puff-back”
  • Melted wiring, burnt smells, or tripped LP/CO alarms
  • Heat exchanger damage suspected (safety-critical)

Quick Reference: RV Furnace Troubleshooting Flow

  1. Thermostat & 12V healthy? (≥12.0–12.6V under blower)
  2. Return/ducts clear? Sail switch closes? (blower starts → then hear clicks)
  3. Igniter sparks & flame lights? (clean probe/align, clear burner/orifice)
  4. Flame stays? (sensor/ground good, ducts open, limit not tripping)
  5. Board/harness if all else passes.

Mastering how to troubleshoot an RV furnace (propane) that won’t ignite gives you reliable heat in shoulder seasons and winter. If you’d rather skip the guesswork, our technicians can test LP pressure, clean burners, verify boards/sensors, and optimize airflow so your furnace lights fast and runs steady—book your heating service at Daisy RV.

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