Short answer: E02 on an HLN diesel heater means the supply voltage is too high. On 8kW rotary-switch models without a screen, the same fault is flashed as blink code 00010. The usual causes are a battery charger connected while the heater runs, or a faulty vehicle charging system (alternator regulator).

Voltage limits — air and coolant heaters differ

• Air heaters (Aerolyn 2kW / 4kW / 8kW): voltage must be below 16 V on a 12 V heater, and below 32 V on a 24 V heater.
• Coolant heaters (Aquano 5K / 10K / 12K / 15K): voltage must be below 18 V on a 12 V heater, and below 32 V on a 24 V heater.

Note the difference: the air-heater limit (16 V) is tighter than the coolant-heater limit (18 V) on 12 V systems. These are different platforms — use the limit for your heater type.

Factory diagnosis

1. Measure the voltage at the heater. It should match battery voltage.
2. Is a battery charger connected? If so, disconnect it — many chargers push a 12 V bank above the heater's limit during charge or desulphation cycles.
3. Check the vehicle charging system — a failed alternator regulator can overvolt the whole system. Correct any problems found.
4. If the measured voltage is actually normal and E02 still appears, replace the ECU.

FAQ

Can I run the heater while a lithium charger is on?
Only if the charging voltage stays below the limit for your heater type (16 V air / 18 V coolant on 12 V systems). If the code appears during charging, disconnect the charger first.

My 8kW heater has no screen — how do I see this code?
Count the status-light flashes: E02 is 00010 — three short, one long, one short (long = 1, short = 0).

Is E02 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 and controller manual (2026 revised editions).