Intergas F004 Fault Code: Causes, Fixes & Repair Costs
What does the Intergas F004 fault code mean?
The F004 code appears on Intergas boilers when the PCB (the boiler's control board) cannot detect a valid flame signal from the burner. This can mean one of two things: the burner is attempting to ignite but the flame sensor isn't picking up the flame, or the boiler is failing to ignite at all. Either way, the boiler locks out as a precaution to prevent unsafe operation. When the fault triggers, the service symbol flashes and F004 is shown on the left-hand display for around 30 seconds before the boiler shuts down.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Faulty or contaminated flame sensor Common
The flame sensor (also called the ionisation probe) monitors the burner flame and relays a signal back to the PCB. Over time, the sensor can become coated in oxidisation or carbon deposits, or the component itself can degrade, causing it to send a weak or absent signal even when a flame is present. This is the single most frequent cause of F004 on Intergas boilers.
- Gas supply not reaching the burner Common
If the gas supply to the property has been interrupted — or the isolation valve on the boiler's gas line has been accidentally turned off — there will be no fuel to ignite. This is worth checking before arranging an engineer visit, as it is a simple thing to overlook.
- Faulty or sticking gas valve Sometimes
The gas valve regulates how much gas flows into the burner. If the valve is worn, partially seized, or failing electrically, it may not open fully — or at all — starving the burner of gas and preventing ignition. Gas valves are mechanical components that wear with age and are a known cause of flame failure faults on Intergas boilers.
- Loose or damaged ignition leads Sometimes
The ignition electrode and its connecting leads create the spark that lights the gas. If a lead has worked loose from vibration, suffered heat damage, or developed a crack in its insulation, the spark may be too weak or may earth out before reaching the electrode, resulting in a failed ignition attempt.
- Carbon build-up on the burner Rare
On older boilers that have not been regularly serviced, carbon deposits can accumulate on the burner surface. In significant amounts, this restricts the gas-air mix and makes it difficult for the burner to sustain a stable flame, causing repeated flame failures and triggering F004.
How to fix it
- Check that your gas supply is active DIY safe
Confirm that other gas appliances in the property (hob, gas fire, etc.) are working normally. Also check that the isolation valve on the pipe leading into the boiler is in the open position — the handle should be parallel to the pipe. If you have a prepayment meter, ensure it has sufficient credit.
- Reset the boiler DIY safe
Press and hold the flashing Service button on the boiler's control panel for approximately two seconds to reset. The boiler will attempt to re-ignite. If it fires up and runs normally, monitor it over the next 24 hours. If F004 returns, do not keep resetting repeatedly — two or three attempts is the limit before you need professional help.
- Do not attempt to inspect or replace internal components yourself Gas Safe engineer
The flame sensor, gas valve, ignition electrode, and connecting leads are all internal boiler components. Inspecting, cleaning, or replacing any of these requires the boiler to be stripped down and involves gas pipework. This work must only be carried out by a Gas Safe registered engineer — it is illegal and dangerous for an unqualified person to do so.
- Contact a Gas Safe registered engineer to diagnose and repair the fault Gas Safe engineer
An engineer will remove and inspect the flame sensor first, as it is the most common culprit — cleaning or replacing it is a relatively straightforward job. If the sensor is not at fault, they will test the gas valve electrically and mechanically, check ignition lead continuity and condition, and inspect the burner for carbon fouling. They will carry out any necessary repairs or component replacements safely and legally.
Parts you may need
- Ionisation / flame sensor probe · from £25
- Ignition electrode assembly · from £35
- Ignition lead set · from £20
- Gas valve · from £150
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £80–£350, depending on the underlying cause.
Frequently asked questions
Can I reset an Intergas F004 fault myself?
Yes, a reset is the one thing you can safely try yourself. Hold the Service button for about two seconds to clear the lockout and allow the boiler to attempt re-ignition. If F004 comes back after one or two resets, stop trying — repeated failed ignition attempts can cause unburnt gas to accumulate, and the underlying fault needs a Gas Safe engineer to diagnose properly.
How much does it cost to fix an Intergas F004 fault in the UK?
Most people pay somewhere between £80 and £350 depending on what's wrong. If the flame sensor simply needs cleaning or replacing, you're likely looking at the lower end — often covered within a standard call-out and labour charge. A gas valve replacement typically costs around £250–£350 including parts and labour, and may take a day or two if the part needs to be ordered. In rare cases where the PCB is at fault, costs can rise to £400–£500 or more, though this is uncommon with F004 specifically.
Why does my Intergas boiler keep showing F004 after I reset it?
If F004 returns quickly after each reset, the boiler is failing to establish or hold a flame every time it tries to light. This points to a persistent component fault rather than a one-off glitch — most likely a degraded flame sensor, a gas valve that isn't opening correctly, or a wiring issue. Each failed attempt is the boiler correctly protecting itself, so repeated resetting won't fix the underlying problem. You need a Gas Safe engineer to investigate.
Is F004 dangerous — should I stop using the boiler?
Intergas boilers lock out when F004 is triggered, so the boiler has already shut itself down as a precaution. While the lockout itself means the boiler is in a safe state, you should not attempt to bypass it or override the safety shutdown. Arrange for a Gas Safe engineer to inspect the boiler before returning it to normal use. If you smell gas at any point, do not reset the boiler — leave the property, open windows, and call the National Gas Emergency Service on 0800 111 999.