Error code
Vaillant Boiler Fault Code F28
The boiler failed during ignition The most likely cause is gas supply interruption or meter issue. Check first: check the boiler display and user controls for obvious demand or supply issues.
Quick answer
F28: what does it mean and how to fix
What does it mean?
The boiler failed during ignition
How to fix first
Check whether other gas appliances appear to have a working supply, without opening the boiler.
Why is this happening?
Gas supply interruption or meter issue
When should I call an engineer?
Call a Gas Safe registered engineer if F28 returns after one reset, other gas appliances work normally, or the boiler keeps attempting ignition without lighting.
What does this error code mean?
Vaillant boiler fault code F28 usually means the boiler has tried to ignite but has not established a safe flame. It is different from Vaillant F29, which is more about flame being lost after the boiler has started.
This code sits in the ignition startup path, including gas supply, ignition electrode, flame sensing, gas valve, fan, flue, and controls.
Start with this safe check: Check whether other gas appliances appear to have a working supply, without opening the boiler. If the code returns, the fault worsens, or the appliance does not behave normally, call a Gas Safe registered engineer if F28 returns after one reset, other gas appliances work normally, or the boiler keeps attempting ignition without lighting.
Symptoms users may notice
- The boiler may try to start but fail before heating or hot water is delivered.
- You may hear ignition attempts followed by lockout.
- The code can appear after a gas supply interruption or boiler restart.
What users often notice
- F28 usually happens at startup, before the boiler has settled into normal running.
Why is this happening?
- Gas supply interruption or meter issue
- Ignition electrode or flame sensing fault
- Air in the gas line after supply work
- Gas valve, fan, flue, or control fault requiring professional diagnosis
What this usually points to
This code sits in the ignition startup path, including gas supply, ignition electrode, flame sensing, gas valve, fan, flue, and controls.
How to fix this safely
- Check whether other gas appliances appear to have a working supply, without opening the boiler.
- Check the boiler display and user controls for obvious demand or supply issues.
- Try one standard reset only if the Vaillant manual allows it.
- Stop further reset attempts if F28 returns.
What not to do
- Do not repeatedly reset the boiler.
- Do not remove the casing or adjust gas, flue, fan, or ignition components.
Common misdiagnoses
- F28 can be assumed to be only a gas meter issue, but repeated F28 with normal gas supply points to boiler-side ignition diagnosis.
Reset steps
- Follow the reset instructions shown on the boiler control panel or in the Vaillant manual.
- Allow one ignition attempt after the reset.
- If F28 reappears, book a Gas Safe registered engineer.
Intermittent vs persistent faults
A one-off F28 after a supply interruption may clear with one permitted reset; repeated F28 should be treated as persistent.
When to call an engineer
Call a Gas Safe registered engineer if F28 returns after one reset, other gas appliances work normally, or the boiler keeps attempting ignition without lighting.
Safety warning
Do not remove the boiler casing or try to work on gas, ignition, or combustion components yourself.
Useful hub links
Related ignition fault codes
Relevant guide
Frequently asked questions
Can I keep resetting a Vaillant boiler with F28?+
No. Try one permitted reset only. Repeated F28 lockouts need a qualified ignition and flame-proving diagnosis.
How is Vaillant F28 different from F29?+
F28 usually means ignition was not established. F29 usually means the boiler lit or was running, then lost flame detection.
Does F28 always mean the gas is off?+
No. Gas supply is one possibility, but electrodes, flame sensing, gas valve, fan, flue, or controls can also cause it.
Can I clean the ignition electrode myself?+
No. That requires opening the boiler casing and must be handled by a Gas Safe registered engineer.
What does F28 mean on a Vaillant boiler?+
F28 usually means the boiler failed during ignition. If it repeats after one safe retry, treat it as a persistent fault.
How to fix F28 on a Vaillant boiler?+
Check whether other gas appliances appear to have a working supply, without opening the boiler. Check the boiler display and user controls for obvious demand or supply issues. Stop and escalate if the code returns immediately.
Why is F28 happening on my Vaillant boiler?+
The most common reasons are Gas supply interruption or meter issue, Ignition electrode or flame sensing fault, Air in the gas line after supply work. Repeated returns usually mean the underlying component or system still needs attention.