Diesel Heater Troubleshooting Guide

This guide covers common issues found in diesel air heaters used in camper vans, motorhomes and off-grid vehicles. It focuses on practical, field-serviceable checks suitable for both DIY installers and general users.

Before You Begin

Always perform checks with the heater powered off (unless testing), and ensure good ventilation when running the unit. It is strongly recommended to keep spare fuses, a glow plug, a fuel filter and basic tools onboard.

1. Heater Fails to Start

Possible Causes

• No power / low battery voltage
• Blown fuse
• Fuel not reaching the heater
• Air in fuel line
• Faulty glow plug
• Controller or wiring fault

Troubleshooting Steps

• Check battery voltage (heater may refuse to start below 11.5–12V).
• Inspect the main fuse and replace if blown.
• Verify fuel pump ticking during startup — no ticking suggests electrical or pump failure.
• Prime or re-prime the fuel line if the heater has recently been serviced or run dry.
• Inspect wiring harness for loose plugs or corrosion.
• Remove and inspect the glow plug; replace if carbon-fouled or damaged.

2. Heater Starts but Shuts Down Shortly After

Possible Causes

• Overheating due to poor airflow
• Blocked air intake or outlet
• Excessive soot in combustion chamber
• Low voltage during run cycle
• Faulty temperature sensor

Troubleshooting Steps

• Ensure the heater has clear airflow into the return and out through the ducting.
• Check for crushed ducting or blocked vents.
• Confirm battery/charging system is providing stable voltage.
• Inspect exhaust and intake for obstructions.
• Run the heater on high for 10–20 minutes to clear carbon buildup.

3. Diesel Smell in the Cabin

Possible Causes

• Fuel leak
• Exhaust leak under vehicle
• Incorrect combustion air intake routing
• Poorly sealed heater baseplate or grommet

Troubleshooting Steps

• Inspect all fuel lines, clamps and filters for leaks.
• Check exhaust pipe and joints for loose clamps or damage.
• Ensure the combustion air intake is external.
• Confirm the floor cut-out and baseplate are fully sealed.
• Stop operating immediately if fumes enter the cabin.

4. Excessive Smoke from Exhaust

White Smoke (unburnt fuel)

• Cold start conditions
• Faulty glow plug
• Carbon buildup
• Blocked air intake

Black Smoke (rich burn)

• Blocked exhaust
• Restricted intake
• Incorrect heater installation angle

Troubleshooting Steps

• Run heater on high to burn off excess fuel.
• Inspect glow plug and burner.
• Check exhaust and intake for obstructions.
• Verify heater mounting angle per manufacturer instructions.

5. Fuel Pump Clicking Too Loud

Possible Causes

• Pump mounted rigidly to metal
• Incorrect mounting angle
• Worn pump

Troubleshooting Steps

• Re-mount using rubber isolators.
• Adjust pump to correct angle.
• Inspect fuel line for vibration transfer.
• Replace pump if noise worsens or delivery becomes inconsistent.

6. Heater Runs but Produces Low Heat

Possible Causes

• Restricted intake or outlet
• Long or compressed ducting
• Low fuel flow
• Dirty burner or heat exchanger
• Low electrical voltage

Troubleshooting Steps

• Inspect ducting for kinks or blockages.
• Check return-air intake is unobstructed.
• Replace clogged fuel filter.
• Run the heater at full power to burn off carbon.
• Measure voltage under load.

7. Error Codes on Controller

Common Error Categories

• E01 / F01 – No flame detected
• E02 / F02 – Overheat
• E03 / F03 – Fan motor fault
• E04 / F04 – Glow plug fault
• E05 / F05 – Low voltage
• E06 / F06 – Fuel pump circuit fault

Troubleshooting Steps

• Consult your heater’s model-specific manual.
• Reset the controller after fixing the underlying issue.
• Inspect wiring harness and connectors.

8. Soot Build-Up or Poor Combustion

Possible Causes

• Running heater mostly on low
• Contaminated diesel
• Blocked intake or exhaust
• Failing glow plug

Troubleshooting Steps

• Run heater at full power for 20–30 minutes (“burn-off”).
• Clean or replace glow plug.
• Inspect burner chamber if performance remains poor.
• Use clean, winter-grade diesel in cold weather.

9. Strange Noises or Vibrations

Possible Causes

• Loose mounting hardware
• Fan motor imbalance
• Worn bearings
• Ducting rubbing against vehicle body

Troubleshooting Steps

• Tighten all bolts and clamps.
• Check duct routing for contact points.
• Listen to identify if noise is fan, pump or combustion-related.
• Replace fan motor if grinding or scraping continues.

10. Heater Won’t Shut Down Properly

Possible Causes

• Controller fault
• Stuck relay
• Wiring short
• Incorrectly installed aftermarket controller

Troubleshooting Steps

• Disconnect and reconnect controller plug.
• Inspect wiring for damage.
• Perform a full power reset (disconnect battery briefly).
• Replace controller if problem persists.

When to Seek Professional Help

Seek qualified service if:

• Exhaust fumes enter the cabin
• Fuel leaks are present
• Error codes reoccur frequently
• Heater repeatedly fails cold starts
• Internal parts (burner, chamber, fan) require teardown

Professional servicing is recommended every 1–2 years depending on usage.