Vaillant F.28: no flame detected when the boiler tried to light
Checked against Vaillant's own documentation: Vaillant: boiler fault codes list and 6 more sources. Last reviewed October 2026. How we check
Check these first, then call an engineer
The boiler tried to light but didn't detect a flame, so it locked out. In winter a common cause is a frozen condensate pipe. Vaillant also lists gas supply problems (such as low gas pressure or a gas meter fault) and ignition or electrical faults.
What you can safely do
- Check your gas supply: does your hob work? If you have a prepayment meter, check it has credit.
- In freezing weather, find the white plastic condensate pipe outside. If it is frozen, pour warm (not boiling) water along it until it thaws.
- Press the reset key for one second. Vaillant says to try this no more than three times.
Call a Gas Safe engineer if
- The boiler still shows F.28 after three resets.
- Your gas supply is fine and the condensate pipe isn't frozen.
- You smell gas at any point. Leave the property and call 0800 111 999.
Which Vaillant boilers show F.28
| Model | What Vaillant's manual says | Source |
|---|---|---|
| ecoTEC pro | Shows F.28 after three failed attempts to light. Press the fault clearance key for one second; if three presses don't clear it, consult a competent person. | Vaillant ecoTEC pro operating instructions (0020244996_01, 2017) |
| ecoFIT pure | The same: F.28 after three failed attempts to light, then up to three resets before calling a competent person. | Vaillant ecoFIT pure 825–835 combi operating instructions (0020230532_03, 2019) |
| ecoTEC plus | Listed in the fault code table as no flame detected during ignition. | Vaillant ecoTEC plus installation and servicing instructions (fault code table) |
What happens before F.28 appears
Vaillant's operating instructions say the boiler tries to light three times on its own. Only after three failed attempts does it lock out and show F.28. So by the time you see the code, the boiler has already retried. That's why Vaillant limits you to three resets.
The causes Vaillant lists
Things you can check: whether gas is reaching your home (your hob works and a prepayment meter has credit), and, in freezing weather, whether the condensate pipe outside has frozen.
Things for a Gas Safe engineer: a closed gas isolator or low gas pressure, air in the gas supply, a blocked air intake, the ignition electrodes, ignition transformer or burner, and wiring faults.
In a cold snap
Vaillant names F.28 and F.29 as the codes that point to a blocked condensate pipe. It says to pour warm water along the frozen part, never boiling water from a kettle, which can crack the pipe. Our frozen condensate pipe guide shows how to find and thaw it.
Applies to Vaillant ecoTEC pro, Vaillant ecoFIT pure, Vaillant ecoTEC plus. Codes can differ between models, so check your manual.