Short answer: E22 on an HLN coolant heater (Aquano 5K / 10K / 12K / 15K) means the water pump is drawing too much current — a short circuit, a stalled or internally shorted pump motor, a damaged or leaking pump, or debris in the coolant pipes jamming the impeller. The blink-code equivalent is 10110. A current measurement separates a bad pump from a bad ECU.

What E22 means

The ECU raises E22 when pump current exceeds 8 A on a 12 V heater or 5 A on a 24 V heater. The brushless pump normally draws 35 W for the first 5 minutes, then drops to 18 W in steady running.

Factory diagnosis

1. Check the wiring for a short circuit.
2. Check the coolant pipes for debris jamming the pump — clear any blockage.
3. Bench-test the pump directly:
   • 12 V heater: apply 12 V to the pump. In the first 5 minutes (35 W phase): current under 2.9 A → the pump is fine, test/replace the ECU; current over 2.9 A → replace the pump.
   • 24 V heater: apply 24 V. Current under 1.46 A → test/replace the ECU; current over 1.46 A → replace the pump.
4. Also inspect for a damaged or leaking pump body — replace if found.

FAQ

Can debris really trigger an electrical fault?
Yes — a jammed impeller stalls the motor, and a stalled motor draws far more current than a spinning one. Flush the coolant circuit before condemning the pump.

Do air heaters get E22?
Air heaters have no water pump — this code belongs to the coolant (hydronic) heaters.

Is E22 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).