Problem: Furnace Won’t Stay Running

Why Won't My Furnace Stay Running?

If your RV furnace starts but won’t stay running, the issue is usually related to flame sensing, airflow, or power delivery.

In many cases, the furnace initially starts correctly, but one of the safety systems shuts the burner down shortly afterward. The blower fan may continue running, or the furnace may repeatedly attempt to restart.

This is one of the most common RV furnace issues in both Suburban and Dometic (Atwood) furnace systems.

The Most Common Cause: Weak or Dirty Igniter Electrode

In most RV furnaces, the igniter electrode performs two important jobs:

  • Creates the spark to ignite the burner
  • Detects the flame after ignition

If the control board cannot properly sense the flame, it shuts the gas valve off for safety — even if the burner briefly lights.

Common Symptoms

  • Furnace lights briefly then shuts off
  • Heat starts but only lasts a few seconds
  • Furnace repeatedly cycles on and off
  • Blower fan continues running after flame shuts down

Why the Electrode Fails

Over time, the electrode can develop:

  • Carbon buildup
  • Corrosion
  • Cracked ceramic insulation
  • Improper gap or alignment

Even small amounts of buildup can weaken the flame signal enough to cause shutdown problems.

The Next Most Likely Cause: Low Voltage

RV furnaces are extremely sensitive to voltage.

If battery voltage drops too low, the blower may still run, but the furnace may not stay lit consistently.

Common Signs of Low Voltage

  • Furnace works intermittently
  • Furnace runs longer when plugged into shore power
  • Blower sounds weak or slow

Check For:

  • Weak battery charge
  • Poor ground connections
  • Corroded terminals
  • Undersized or damaged wiring

Another Common Cause: Restricted Airflow

Poor airflow can trigger safety shutdowns and prevent the furnace from staying operational.

Common Airflow Problems

  • Dirty blower wheel
  • Blocked ducts or vents
  • Restricted intake or exhaust
  • Weak blower motor

When airflow drops too low, the furnace may overheat and shut the burner down.

Limit Switch Problems

The limit switch protects the furnace from overheating.

If it becomes weak or overly sensitive, it may shut the burner down too early.

Signs of a Bad Limit Switch

  • Furnace heats briefly then shuts off
  • Blower continues running
  • Furnace repeatedly restarts

Less Common Cause: Failing Control Board

If the control board cannot properly process the flame signal or maintain ignition timing, the furnace may shut down unexpectedly.

This is usually less common than:

  • Electrode issues
  • Low voltage
  • Airflow problems

Recommended Repair Order

For the fastest and most affordable repair:

  1. Clean the igniter electrode
  2. Check electrode alignment and wiring
  3. Verify battery voltage
  4. Inspect airflow and blower condition
  5. Replace the electrode assembly
  6. Move to limit switch or control board diagnosis if needed

Could it be the Sail Switch?

The sail switch is a potential cause of a furnace that won’t stay running, especially if airflow is borderline.

However, for a furnace that:

  • starts normally
  • ignites successfully
  • then shuts off afterward

…the sail switch is usually less likely than the igniter electrode/flame sensing issue.

That’s because the sail switch’s primary job is to prove airflow before ignition occurs. If the burner already lit, the sail switch already did its job initially.

Pro Tip

If your furnace is older, many RV owners replace both:

  • Igniter electrode
  • Limit switch

These are inexpensive wear items and commonly responsible for intermittent furnace shutdown problems.