Webasto diesel heaters are known for their reliability in off-grid and mobile environments, especially among van and truck owners. However, even reliable systems can fail if improper troubleshooting steps are taken. In this case, a van owner encountered Flash Code 08 - and damaged the Webasto fuel pump in the process.

Webasto diesel heaters are known for their reliability in off-grid and mobile environments, especially among van and truck owners. However, even reliable systems can fail if improper troubleshooting steps are taken. In this case, a van owner encountered Flash Code 08 - and damaged the Webasto fuel pump in the process.

A customer contacted us with a clear symptom: his Webasto 2000 STC heater would start but failed to ignite. The controller indicated the fault: Flash Code 08.

Many users search for answers when their Webasto diesel heater fuel pump is not working, particularly after long downtime periods or following unsupported troubleshooting attempts.

On Webasto heaters, Flash Code 08 indicates a short circuit in the fuel dosing pump. This typically means the pump is no longer operational due to an internal electrical failure and must be replaced.

The heater had been unused for a prolonged period. Believing that air had entered the fuel line - a common issue after long downtime - the user attempted a manual test by applying direct 12V power to the fuel pump terminals.

While this approach can be used with some Eberspacher pumps, where short 12V impulses can be applied for diagnostic purposes and to see if the pump works (looking for that ticking sound), it is not safe for Webasto pumps.

Webasto fuel pumps rely on precise electrical pulses sent by the Webasto heater ECU. These pulses control the timing and volume of fuel delivery. Applying a continuous 12V current overrides the ECU’s control and results in an electrical short within the pump.

In this case, the user’s action caused the pump to fail electrically, triggering Flash Code 08 and leaving the heater non-functional.

While the failure occurred in a Webasto 2000 STC, the same risks apply across other Webasto models like

• Air Top EVO 40
• Air Top EVO 55
• Thermo Top Series
• Thermo Pro Series
• Other Webasto heaters

These heaters all use ECU-managed fuel dosing. Applying a constant voltage directly to the pump can cause irreversible internal damage.

To avoid similar situations:

• Do not apply direct voltage to Webasto fuel pumps
• If the heater fails to ignite, contact Webasto or Heatso support for approved troubleshooting procedures
• Operate the heater monthly for 20–30 minutes on high to maintain system circulation and prevent air from entering the fuel line
• After storage periods, inspect the fuel system for blockages or air bubbles
• Avoid running the heater when the fuel tank is running low.

If you’re seeing Webasto Flash Code 08 or if your Webasto fuel pump is not operating, avoid unverified testing methods. A simple misstep can lead to costly repairs or component replacement. You can also read more about the Webasto fault codes.