Short answer: E06 on an HLN air heater means the ECU has detected a short circuit on the overheat sensor. If the overheat sensor reads less than 500 Ω without combustion, the sensor is shorted. On 8kW rotary-switch models without a screen, the same fault is flashed as blink code 00110.

What E06 means

The overheat sensor is the heater's thermal safety. A shorted sensor would feed the ECU a falsely high temperature reading, so the ECU raises E06 and stops instead of trusting it. On air heaters the overheat sensor and the flame sensor are supplied together as a combo sensor.

Factory diagnosis (Aerolyn 2kW / 4kW / 8kW)

1. Measure the overheat sensor's resistance (heater cold, no combustion). Less than 500 Ω → the sensor is shorted — replace it.
2. To confirm which side the fault is on: disconnect both the flame and overheat sensors from the ECU and scan for fault codes again.
3. If the code changes to E05 (open circuit — expected with the sensor unplugged), the short was in the sensor: replace the combo sensor.
4. If E06 is still displayed with the sensors disconnected, test the ECU and replace it if necessary.

FAQ

Why does E05 appearing during the test mean the sensor is bad?
With the sensor unplugged the ECU should see an open circuit (E05). If it does, its measuring circuit works — the short it saw must have been in the sensor. If it still sees a short with nothing connected, the fault is on the ECU side.

My 8kW heater has no screen — how do I see this code?
Count the status-light flashes: E06 is 00110 — two short, two long, one short (long = 1, short = 0).

Is E06 the same on other heater brands?
No. Fault-code tables are brand-specific — this table applies to HLN heaters only.

All HLN fault codes in one place: HLN Diesel Heater Error Codes Explained (E01–E32). Source: HLN factory service manual (2026 revised editions).