Saunier Duval F1 Fault Code: Ignition Failure Explained
The F1 fault code on a Saunier Duval boiler indicates that the appliance has failed to establish a flame after one or more ignition attempts. Unable to detect a stable flame, the boiler shuts itself down as a safety precaution — a state known as lockout. A flashing red indicator light typically accompanies the code on the display. The boiler will not restart automatically; it must be investigated and manually reset before it will attempt to fire again.
General guidance only — not a substitute for professional advice. 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.
What does the Saunier Duval F1 fault code mean?
The F1 fault code on a Saunier Duval boiler indicates that the appliance has failed to establish a flame after one or more ignition attempts. Unable to detect a stable flame, the boiler shuts itself down as a safety precaution — a state known as lockout. A flashing red indicator light typically accompanies the code on the display. The boiler will not restart automatically; it must be investigated and manually reset before it will attempt to fire again.
Common causes
- Gas supply interruption or low gas pressure Common
If the gas isolation valve is closed, partially restricted, or if there is a wider supply problem on your street, the boiler simply has no fuel to ignite. Even when gas is present, insufficient pressure at the burner can be enough to prevent a flame forming. Checking whether your gas hob or another appliance lights normally is a quick way to rule this in or out.
- Worn, dirty, or misaligned ignition and ionisation electrodes Common
The ignition electrode creates the spark that lights the burner, while the ionisation electrode confirms that a flame is present. Over time, carbon deposits build up on both probes, reducing the quality of the spark or making flame detection unreliable. The boiler makes several ignition attempts, detects nothing, and locks out with F1. Electrode wear is one of the most frequently identified causes of this fault code.
- Blocked or contaminated burner Sometimes
A build-up of carbon residue or general debris on the burner surface can prevent the gas-air mixture from igniting correctly. This is more common on boilers that have not had a recent service and may be accompanied by unusual smells or a yellow flame before the lockout occurs.
- Flue obstruction or fan problem Sometimes
The combustion fan must run at the correct speed to draw fresh air in and exhaust gases out before ignition is permitted. A partial flue blockage — caused by debris, a bird nesting, or a collapsed flue terminal — or a fan that is struggling to reach speed will disrupt the air-to-gas ratio. Some Saunier Duval models detect this via an air pressure switch and prevent ignition entirely, triggering F1.
- Air pressure switch fault Sometimes
The air pressure switch monitors fan-generated airflow and only signals the PCB to proceed with ignition once satisfactory airflow is confirmed. A faulty or sticking switch can report inadequate airflow even when the fan is working correctly, causing a preventive lockout. This is more likely to appear at the start of the heating season after a long summer lay-off.
- Faulty gas valve Rare
If the gas valve is stuck closed or not opening fully in response to the ignition command, no gas will reach the burner regardless of how good the spark is. The result is indistinguishable from a gas supply failure and requires a Gas Safe engineer to diagnose properly.
- PCB (printed circuit board) failure Rare
In a small number of cases the main control board itself is at fault — either failing to send the ignition command correctly, or misreading the signal from the ionisation electrode. PCB faults tend to show up on older appliances or those that have experienced an electrical surge.
How to fix it
- Check that your gas supply is working DIY safe
Go to your gas meter and confirm that the isolation valve handle is in line with the pipe (open position). Then try lighting a gas hob or another gas appliance. If nothing else on the gas supply is working either, there may be a network interruption — contact your gas supplier before doing anything else with the boiler.
- Check the boiler's system pressure DIY safe
Look at the pressure gauge on the boiler — it should read between 1.0 and 1.5 bar when cold. If it has dropped below 0.8 bar, top it up using the filling loop (usually a braided flexible connector beneath the boiler) until it reaches around 1.2–1.5 bar, then close the filling loop valves. Consult your boiler's user guide for the exact filling loop location on your model.
- Reset the boiler DIY safe
Once you have confirmed gas is on and pressure is correct, press and hold the reset button (often marked with a flame or reset symbol) for a few seconds until the boiler attempts to restart. Allow a full ignition cycle to complete before judging whether it has cleared. If the boiler locks out again immediately, do not reset it more than two or three times in quick succession — repeated failed ignition attempts will not help and may indicate a more serious underlying issue.
- Call a Gas Safe registered engineer to inspect the electrodes and burner Gas Safe engineer
If the boiler continues to lock out with F1 after the checks above, the most likely culprits are the ignition or ionisation electrodes and the burner. An engineer will remove the burner assembly, inspect the electrode tips for carbon fouling or damage, clean or replace them, and check electrode gap and alignment. The burner itself will be checked for contamination and cleaned if necessary. This is not a DIY task — it involves gas components inside the appliance.
- Have the flue and fan inspected Gas Safe engineer
An engineer will check the flue terminal externally for obstructions and inspect the combustion fan internally for correct operation and speed. A partial blockage in the flue or a fan running below specification can cause intermittent F1 faults that are easy to overlook. The air pressure switch will also be tested at this point.
- Gas valve testing and replacement if required Gas Safe engineer
If gas supply, electrodes, burner, and flue are all confirmed to be in order, the engineer will use diagnostic equipment to test whether the gas valve is opening correctly in response to the ignition command. Gas valve work is strictly Gas Safe registered engineer territory and must never be attempted by anyone without the appropriate qualifications.
- PCB diagnosis and replacement if required Gas Safe engineer
If all other components test correctly, the PCB may be sending an incorrect ignition command or misinterpreting the flame signal. An engineer can test PCB outputs with appropriate meters. Replacement boards for Saunier Duval models can be sourced and fitted in one visit if available, but on boilers over ten years old it is worth discussing whether replacement of the boiler is a more cost-effective option than a new PCB.
Parts you may need
- Ignition electrode · from £45
- Ionisation (flame detection) electrode · from £40
- Ignition lead / HT lead · from £25
- Burner (replacement) · from £120
- Combustion fan · from £140
- Air pressure switch · from £35
- Gas valve · from £220
- PCB (main control board) · from £290
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 £150–£380, depending on the underlying cause.
Frequently asked questions
Can I reset an F1 fault myself, or do I always need an engineer?
You can safely reset the boiler yourself after first checking that the gas is on and the system pressure is correct. A reset resolves the fault in a significant proportion of cases — particularly if the lockout was triggered by a momentary gas supply dip. However, if the boiler locks out again after one or two resets, stop resetting and call a Gas Safe registered engineer. Repeated ignition attempts without resolving the underlying fault will not fix anything and could mask a more serious problem.
How much does it typically cost to fix a Saunier Duval F1 fault code?
For the most common causes — electrode cleaning or replacement and a burner service — expect to pay roughly £150–£300 including labour. A gas valve replacement usually comes in at around £200–£350 all in. PCB replacement is less common but significantly more expensive, often £400–£650 including parts and labour; if your boiler is already eight to ten years old or more, it is worth getting a new boiler quote alongside a PCB quote before committing.
Why does my Saunier Duval keep showing F1 at the start of winter?
Seasonal F1 faults are common after the boiler has sat unused over summer. Debris or insects can partially block the flue terminal, and the air pressure switch or fan can become sluggish after months without running. A pre-winter annual service — where an engineer inspects the burner, electrodes, fan, and flue — is the most effective way to prevent this pattern repeating each year.
Is the F1 fault code dangerous?
The lockout itself is a safety feature, not a danger sign — the boiler has detected that it cannot establish a safe flame and has shut down to prevent unburnt gas from accumulating. As long as you do not attempt to repeatedly reset the boiler or interfere with gas components yourself, there is no immediate danger. Do not attempt to dismantle any part of the gas system. If at any point you smell gas, do not reset the boiler, open windows and doors, leave the property, and call the National Gas Emergency Service on 0800 111 999 immediately.