HVACopediaBosch · Boiler
8.F Service function 8.F - permanent ignition test
What the display is showing
Gives continuous sparking without gas so the ignition parts can be tested. Values 00 off, 01 on. Never leave it on for more than 2 minutes at a time because it can damage the ignition transformer.
Applies to: Greenstar ZBR/ZWB 21-42-3A wall-hung boilers and ZWB 28-42-3A combis
What to do
- Reach the second level and scroll to 8.F
- Set 01, test, then set 00
Models that show this code
4 models in Bosch Greenstar
Other codes on the same units
- 7.b Service function 7.b - 3-way valve to center position
- 8.A Service function 8.A - software version
- 8.C Service function 8.C - gas burner control (GFA) status
- 8.E Service function 8.E - restore factory settings
- 8.b Service function 8.b - code plug number
- 8.d Service function 8.d - gas burner control (GFA) fault
- 9.A Service function 9.A - constant operating mode
- 9.C Service function 9.C - current boiler output
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Source: Bosch Greenstar wall ZBR-ZWB 21-42-3A service 6721853955 (2025-11) (same content in combi service 6721853953), 11.3 Description of the service functions pp.59-64. Summarized in our own words; check the original manual for your model.
For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.