Vaillant F28 fault code: what it means and what to do

What does the Vaillant F28 fault code mean?

Smell gas? Do not reset the boiler. Call the National Gas Emergency Service on 0800 111 999 first, open windows, turn the gas off at the meter if you can reach it safely, and keep away from switches and naked flames.

F28 on a Vaillant boiler means it tried to light, did not detect a flame, and locked out for safety. Check that gas is reaching your home, that a prepayment meter has credit and, in cold weather, that the outside condensate pipe is not frozen. Then reset the boiler once. If F28 comes back, stop and book a Gas Safe registered engineer.

Vaillant's own definition of F28 is: "The flame signal was not detected during the ignition phase." In plain terms, the boiler asked for gas, tried to spark it, saw no flame and shut the gas off rather than keep trying.

The lockout is the safety system working, not a sign the boiler is about to fail for good. But it will not clear itself. On a combi boiler the same burner heats your radiators and your hot water, so you will have neither until the cause is found.

F28 or F29?

F28 means the boiler never lit at start-up. F29 means it did light, lost the flame while running and could not relight. The safe checks overlap, but if your display shows F29, read our Vaillant F29 guide instead.

Key facts

The short version, before the detail.

• Meaning: "The flame signal was not detected during the ignition phase." That is Vaillant's wording for F28.
• Safe homeowner checks: other gas appliances, prepayment meter credit, the gas being on at the meter, a frozen condensate pipe, and one reset.
• Engineer-only: the ignition electrode, the gas valve, gas pressure at the boiler, the flue and the circuit board (PCB).
• F28 is not a water pressure code. Low water pressure is not among the F28 causes on Vaillant's UK fault code page, so topping up the pressure is not an F28 fix.
• A smell of gas comes before everything else: 0800 111 999, and do not reset.

What causes F28, and who deals with it

What you can safely check yourself

These checks all stay outside the boiler casing. Do not take the front panel off: the electrode, gas valve and wiring inside are a Gas Safe registered engineer's job. Work through the checks in order.

1. Write down the code and the boiler model from the data plate. Whoever comes out will ask for both.

2. Try another gas appliance, such as the hob. If nothing gas-powered works, the problem is the supply into your home, not the boiler. If you have no other gas appliance, go straight to the meter checks.

3. Check the meter. On a prepayment meter, check there is credit and top up if needed. On any meter, check the gas is turned on. If the meter has credit and the gas is on but nothing gas-powered works, contact your gas supplier, because the meter itself may be at fault.

4. In cold weather, check the condensate pipe. It is the white or grey plastic pipe that leaves the boiler and usually runs through the nearest outside wall to a drain. If it is frozen and you can reach it from the ground, pour warm water slowly along it until the ice clears or the pipe drains. Vaillant's advice is: "Do not use boiling water from a kettle, as this can damage or crack the pipe". Never use a ladder or a naked flame.

5. Reset the boiler once, following the reset step in your Vaillant user manual. If the boiler lights and stays running, you are done. If F28 comes back, stop. Pressing reset again and again does not fix an ignition fault.

If your gas meter was recently changed or the gas supply was off for a while, tell the engineer. Air in the gas supply can also cause F28, and an engineer can deal with it safely.

What a Gas Safe registered engineer checks

If F28 returns after one reset, the cause is inside the casing or on the gas side. It helps to know what a proper visit looks like, so you can tell the job is being done in order.

The checks follow the causes in the table above. On the gas side: the gas pressure reaching the boiler, and any air in the line. On the ignition side: the condition and position of the ignition electrode, and its lead and connections. Then the condensate trap and pipe run for a blockage, and the flue for anything stopping the boiler from breathing. The gas valve or the PCB should only be blamed once those check out.

You can save diagnosis time by telling them three things: whether other gas appliances were working, whether the code appeared after a frosty night, and what the boiler did before it locked out, for example repeated clicking. Before any part is ordered, ask which part they have diagnosed and what it will cost.

You can check that an engineer is registered on the Gas Safe Register before they start.

Does Smart Plan cover an F28 fault?

Not one your boiler is showing today. A Smart Plan cover plan is for future breakdowns, so a fault that is already there when you join is not covered.

For next time, Smart Plan boiler and central heating cover includes parts and labour up to a repair limit set out in the terms. The limit depends on the age of your boiler, and if a repair costs more than the limit, you pay the difference.

Vaillant also sells its own repair and service options. To see how they compare with a cover plan, read our guide to Vaillant boiler cover and repair costs.

Some F28 causes sit outside the plan. The terms exclude repairs relating to flues and repairs for damage caused by frost. If the PCB or heat exchanger fails, the terms treat the boiler as beyond economic repair, and a contribution set out in the terms applies instead of a repair.

A £95 call-out fee may apply, but only in the situations set out in the terms. Call-outs run Monday to Friday 08:00 to 18:00, unless it is an emergency breakdown as set out in the terms. Smart Plan is a service plan, not insurance, from UK Boiler Company Ltd, trading since 2014. To talk it through, call 0333 772 6247.

Cover the next breakdown: get a call back

A cover plan is for the next breakdown, not a fault you already have today. Get a free call back to set up cover for next time. We aim to call you back within one working day, Monday to Friday 08:00 to 18:00. It's a service plan, not insurance.

Helpful links

• All Vaillant fault codes
• Vaillant F29 flame-loss fault
• Vaillant F75 pump and pressure fault
• Vaillant F22 low water pressure
• Boiler ignition lockout explained
• Boiler not firing up
• Boiler fault codes by manufacturer
• Boiler & central heating cover
• Vaillant's official boiler fault codes
• Vaillant's guide to the F28 code
• Check an engineer on the Gas Safe Register