Short answer: E11 on an HLN diesel heater means a temperature-sensor short circuit — but which sensor depends on your heater type: on air heaters it is the inlet air temperature sensor; on coolant heaters it is the water temperature sensor (coolant heaters have no inlet-air sensor). On 8kW rotary-switch models the same fault is flashed as blink code 01011.

What E11 means

The ECU reads the temperature sensor's resistance. When that resistance falls out of the acceptable range on the low side — a short — the ECU can no longer regulate temperature and raises E11. A related failure sign on coolant-heater sensors is melted or peeling potting compound on the sensor body.

Factory diagnosis

Air heaters (Aerolyn 2kW / 4kW / 8kW)

1. E11 indicates a short on the inlet air temperature sensor. Test the ECU and replace it if necessary.

Coolant heaters (Aquano 5K / 10K / 12K / 15K)

1. Remove the control unit and unplug the water temperature sensor.
2. Test the sensor's resistance. If it reads above 2000 kΩ or below 3 kΩ, the sensor is damaged — replace it.
3. Inspect the sensor body: melted or peeling potting compound also means replacement.
4. If the sensor tests fine, test the ECU and replace it if necessary.

FAQ

What's the difference between E11 and E12?
E11 is a short circuit (resistance too low); E12 is an open circuit (resistance too high). Same sensor, opposite electrical failure — see the E12 guide.

Is this the sensor in the controller?
No. The room-temperature sensor built into the LCD controller is separate — its own faults show as E1/E2 in the centre of the controller screen, not as E11 at the bottom-left.

Is E11 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).