Short answer: E29 on an HLN air heater (Aerolyn 2kW / 4kW / 8kW) means the blower motor speed is below 300 rpm. On 8kW rotary-switch models the same fault is flashed as blink code 11101. The causes range from a physical restriction to a mounting problem — and one documented case was simply a power supply that couldn't deliver enough current.

What E29 means

The ECU monitors blower rpm continuously. If the motor can't reach or hold 300 rpm, combustion air delivery is unreliable, so the heater stops and raises E29.

Factory diagnosis

1. Measure the blower speed with a non-contact RPM meter.
2. If the rpm is low, check for restrictions or blockage in the air path. If there are none, work through the E21 remedies (motor connection, direct motor test).
3. Check the mounting surface: if the floor is uneven, tightening the heater body down can distort the housing and make the motor bind. Loosen the bolts and re-test on a flat surface.
4. Test the ECU and replace it if necessary.

A real-world case: the power source, not the heater

In a case documented by our support team, a 2kW heater clicked once at start-up, sat silent for about 30 seconds, then showed E29. The heater was fine — the power source could only supply 10 A at 12.8 V, while the heater draws up to 15 A (180 W) during start and shutdown (glow phase). On a current-limited supply the blower can't spin up, and E29 is the result. If you are running from a bench supply, a small lithium pack with a conservative BMS, or a long thin feed wire, verify it can actually deliver 15 A before suspecting the heater.

FAQ

How is E29 different from E21?
Both are blower-motor faults. E21 is raised on motor current/drive problems; E29 specifically means measured speed stayed below 300 rpm. E29 diagnosis borrows the E21 remedies once blockage is ruled out.

My 8kW heater has no screen — how do I see this code?
Count the status-light flashes: E29 is 11101 — three long, one short, one long (long = 1, short = 0).

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