Webasto: why service code 03 and F03 are different things
Updated: 2026-11-10
In short. Webasto has two code systems: F00-F15 on the timer and hexadecimal service codes in the workshop software. The digits coincide, the meaning does not: service 03 is flame-out, F03 is voltage. A driver needs the F-code and the model of the heater.
Where the confusion comes from
One F-code on the timer groups several service codes. On the Air Top 2000 ST service code 03 is flame-out, which the timer shows as F02. F03 is a voltage problem, with service codes 84 and 04. The Thermo Top Evo table has no service code 03 at all.
Air Top 2000 ST F-codes
| On the timer | What happened |
|---|---|
| F00 | Control unit fault |
| F01 | No start |
| F02 | Flame-out |
| F03 | Voltage: below 10.5 V (21 V on a 24 V system) for more than 20 s or above 16 V (32 V) for more than 6 s |
| F04 | Flame before combustion starts |
| F05 | Flame sensor (petrol only) |
| F06 | External temperature sensor |
| F07 | Metering pump |
| F08 | Drive: combustion and heating air fan |
| F09 | Glow plug |
| F10 | Overheating |
| F11 | Overheat sensor |
| F12 | Heater lock-out |
| F14 | Overheat sensor installed incorrectly |
| F15 | Setpoint potentiometer |
This model has no F13.
What changes on the Thermo Top Evo
The numbers are the same, but some meanings differ:
| Code | Air Top 2000 ST | Thermo Top Evo |
|---|---|---|
| F11 | overheat sensor | coolant pump |
| F14 | overheat sensor installed incorrectly | overheat sensor |
| F15 | setpoint potentiometer | glow plug circuit |
| F13 | none | vehicle fan |
| F16 | none | high exhaust temperature |
| F17 | none | exhaust sensor |
| F05, F12 | present | absent |
F03 on the Thermo Top Evo is also about the on-board voltage. The repair table labels it "too high", the user manual "too low or raised"; for the driver it is one thing: check the supply voltage. The conclusion: read an F-code only together with the heater model.
How the driver sees the code
- Combined timer on the Air Top 2000 ST: a code number on the screen until the fault is cleared; the manual advises contacting a Webasto service.
- ON indicator without a display: 5 seconds of rapid flashing, then the number of long flashes equals the F-code number (F04 is four long flashes). Plain rapid flashing is F00.
- MultiControl and SmartControl on the Thermo Top Evo: F01-F15 on the display, while F16-F19 show as "- -". Codes of the form TXX belong to the controller itself.
- W-bus and analog connection on the Thermo Top Evo: hexadecimal Hxx numbers over W-bus, Fxx over analog.
Telestart and ThermoCall controllers show neither the F-code number nor the fact of a heater fault, only the state of the link, battery and module. ThermoCall has a general warning (the heater does not execute the command, service needed). The F-code comes from the heater itself or the indicator in the cab.
What you can do and when to see a workshop
- identify the heater model and the type of controller;
- for F03, inspect the terminals and charge the battery;
- do not compare the number with the service-code table: use the table for your model.
Factory manuals leave the driver little to do. The Webasto instruction directly advises contacting a service for any number code on the timer. Diagnostics are needed for F00, F07, F08, F09, F10 and F11: the control unit, pump, drive, glow plug and overheating.
Questions and answers
Are service code 03 and F03 the same?
No. On the Air Top 2000 ST service 03 is flame-out, which the timer shows as F02. F03 is the on-board voltage.
Why does the same F-code mean something else on the Thermo Top Evo?
The code tables differ between models. For example F11 is the overheat sensor on the Air Top 2000 ST and the coolant pump on the Thermo Top Evo.
Will a Telestart or ThermoCall controller show an F-code?
No, they show the link, battery charge and module state. The F-code comes from the heater or its indicator.
What does the number of long flashes on the ON indicator equal?
The F-code number: after 5 seconds of rapid flashing, four long flashes are F04. Plain rapid flashing means F00.
Code pages on the site
- F03 - on-board voltage
- F02 - flame-out
- F07 - metering pump
- F08 - fan drive
- F09 - glow plug
- F10 - overheating
- All Webasto codes
Checked against manufacturer manuals and tables; the same facts as in our videos and articles. The decision to drive remains with the driver.
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