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Vaillant Boiler F.28 Error Code
Boiler failed to light on Vaillant boilers.
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The boiler tried to light and never saw a flame. Newer ecoTEC plus models give up after five attempts and lock out. A closed gas valve, a gas meter problem or no credit on a prepayment meter is often all it is, and on condensing boilers a frozen or blocked condensate pipe can cause it too. The rest of the list (ignition electrode, gas valve, flue, wiring, PCB) is engineer territory.
Compatible models
Listed on Vaillant's UK fault code page and in the manual for the ecoTEC plus VU 126 to 356/6-5 OVZ boilers; the operating manual for current ecoTEC plus VU, VUW and VUI ../1-5 models shows it as F.028.
Also shown as
Current ecoTEC plus models show it as F.028. It's a lockout, so the boiler stays off until you reset it.
Difficulty
Start with the safe checks below; a worn part may need replacing.
Not sure you are reading the code right? See how to read Vaillant boiler codes.
How to fix Vaillant F.28
Check the gas is getting through
Try the gas hob or another gas appliance. If that won't light either, look at the meter: a prepayment meter may be out of credit or need its emergency credit switched on, and the lever on the meter should line up with the pipe. Make sure the gas stopcock under the boiler is open too.
Look at the condensate pipe in cold weather
Find where the white or grey plastic pipe leaves the house. If it's frozen, pour warm water (never boiling, which can crack it) along the frozen section or hold a hot water bottle against it until the ice clears, then try the reset.
Reset the boiler
Hold the reset button for more than 3 seconds and listen for it to try to light. Vaillant allows up to three attempts.
When to call a technician
Gas supply fine, condensate clear and it locks out again after three resets: book a Gas Safe registered engineer (RGII in Ireland) to test the ignition and gas side. Smell gas at any point and you stop, get out and call your gas emergency number.
Parts linked to F.28
These are the parts an engineer usually checks for this code. They sit inside the sealed casing, so leave them to a Gas Safe registered engineer.
- Gas valve and injector
- Ignition electrode and spark generator
- Flame sensor (flame detection electrode)
- Condensate pipe and trap
- PCB (main control board)
Frequently asked questions
Which Vaillant models show the F.28 code?
Listed on Vaillant's UK fault code page and in the manual for the ecoTEC plus VU 126 to 356/6-5 OVZ boilers; the operating manual for current ecoTEC plus VU, VUW and VUI ../1-5 models shows it as F.028.
Can I fix Vaillant F.28 myself?
Only the outside checks. The steps above are the ones Vaillant's user instructions allow; if they don't clear F.28, the fix is inside the boiler and needs a Gas Safe registered engineer (RGII in Ireland).
Other Vaillant boiler codes
- F.22Water pressure in the heating system is too low
- F.29Flame went out and the boiler couldn't relight
- F.20Overheat safety cut-out has tripped
- F.23Too big a gap between flow and return temperature
- F.24Temperature rising too fast
- F.25Flue gas temperature too high
- F.27Flame detected with the burner off
- F.75No pressure rise when the pump starts
- F.00Flow or return temperature sensor not reading
- F.10Temperature sensor short circuit
- F.13Hot water cylinder sensor short circuit
- F.32Fan speed out of range
- F.61Gas valve control fault
- F.62Flame took too long to go out
- F.68Unstable flame
- F.70Invalid device code after a repair
- F.83Dry fire: no temperature change when the burner lit
Last reviewed 2026-10-21. Codes and steps can vary by model; check your owner's manual.