Saunier Duval F.02 Fault Code: Causes, Fixes & Repair Costs
What does the Saunier Duval F.02 fault code mean?
The F.02 code (sometimes displayed as F2) signals that your Saunier Duval boiler has detected a problem with its airflow or combustion ventilation circuit. The boiler's control board monitors the extraction fan and air pressure switch continuously; if it cannot confirm that flue gases are being safely expelled, it triggers a safety lockout to eliminate any risk of carbon monoxide building up inside your home. The boiler may attempt an automatic restart after roughly 15 minutes, but if the underlying fault remains, F.02 will return. While locked out, the boiler will not provide heating or hot water.
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
- Blocked or obstructed flue terminal Common
The most frequent trigger for F.02. Debris such as bird nests, leaves, soot build-up, or moss can partially or completely block the flue outlet on the outside wall or roof. Without a clear path for exhaust gases to escape, the boiler cannot maintain safe combustion and shuts down. A quick visual check from outside may reveal obvious blockages at the flue terminal.
- Faulty or failed extraction fan Common
The combustion fan creates the negative pressure needed to draw air in and push flue gases out. If the fan motor has seized, is spinning too slowly, or has an electrical fault, the air pressure switch will not register the expected pressure differential and the boiler locks out. You may notice the boiler is completely silent when it tries to fire up, or you may hear an unusual noise from the fan.
- Faulty air pressure switch (pressostat) Common
The pressure switch is a small sensor connected to the fan by thin rubber tubes. It confirms that the fan is generating the correct airflow before allowing ignition to proceed. A perforated diaphragm, corroded electrical contacts, a disconnected sensing tube, or a blocked tube can all cause the switch to send an incorrect signal to the PCB — even if the fan itself is perfectly healthy.
- Frozen condensate pipe Sometimes
In cold weather the plastic condensate pipe that runs outside can freeze solid, causing a blockage that backs up through the system and disrupts airflow monitoring. This is particularly common during overnight frosts. An ice-covered section of pipe visible on an external wall is a strong indicator.
- Blocked or obstructed air vents Sometimes
If the boiler is installed in a cupboard or utility room, ventilation grilles must remain clear at all times. Blocking these grilles — even with boxes or clothes — reduces the air available for combustion, which can be enough to trip the airflow fault.
- Wiring or connector fault Rare
The electrical circuit linking the fan, pressure switch, and PCB relies on secure, corrosion-free connections. Heat, age, or damp can loosen connectors or degrade wiring insulation, producing intermittent faults that mimic a mechanical airflow problem. This is more common on older appliances.
How to fix it
- Check your gas supply DIY safe
Make sure other gas appliances in your home — cooker, gas fire — are working normally. If nothing gas-powered is working, the issue may be with your gas supply rather than the boiler. Contact your gas supplier if the supply appears to be off.
- Inspect the flue terminal from outside DIY safe
Go outside and look at the point where the flue exits the building. Check for obvious obstructions such as bird nests, accumulated leaves, or visible ice blocking the opening. Do not attempt to remove anything yourself — if you can see a blockage, report it to a Gas Safe engineer who can clear it safely.
- Check ventilation grilles around the boiler DIY safe
Ensure that any air vents or grilles in the room or cupboard where the boiler is located are completely unobstructed. Remove any objects that may have been placed in front of them and make sure the boiler cupboard door has not been sealed up.
- Thaw a frozen condensate pipe if applicable DIY safe
If the weather is freezing and you can see an iced-up section of plastic pipe running outside your property, carefully pour warm (not boiling) water along the frozen section until it clears. Never use a naked flame to thaw the pipe. Once thawed, proceed to reset the boiler.
- Listen for the fan when attempting a restart DIY safe
Press the reset button on the boiler (consult your user manual for the exact location — it is usually a button marked with a flame or reset symbol). When the boiler tries to fire up, listen carefully. A healthy fan produces a clear, consistent whirring sound. Complete silence or an unusual grinding noise suggests the fan itself may be at fault. Attempt a reset no more than two or three times.
- Call a Gas Safe registered engineer Gas Safe engineer
If the F.02 fault returns after your basic checks and a couple of resets, the problem requires professional diagnosis. An engineer will test fan speed and electrical supply, inspect and test the air pressure switch and its sensing tubes, examine internal wiring and connectors, and check the flue for blockages that are not visible from outside. Do not continue resetting the boiler repeatedly — persistent lockouts can cause additional component damage over time, and an unresolved airflow fault carries a genuine carbon monoxide risk.
Parts you may need
- Extraction fan assembly · from £130
- Air pressure switch (pressostat) · from £45
- Pressure switch sensing tubes / hoses · from £12
- Flue terminal guard / cowl · from £20
- Fan wiring harness · from £30
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 £120–£350, depending on the underlying cause.
Frequently asked questions
Can I reset the boiler myself when F.02 appears?
Yes, you can attempt a reset — but limit yourself to two or three attempts. If F.02 clears and does not return, the fault may have been a temporary airflow disruption (for example, a brief gust of wind at the flue terminal or a momentarily frozen condensate pipe). If the code comes back each time you reset, stop resetting and call a Gas Safe engineer. Repeated resets without resolving the root cause will not fix the problem and could stress other components.
How much does it cost to fix a Saunier Duval F.02 fault?
For the most common causes — pressure switch replacement or fan replacement — most homeowners pay between £120 and £350 including parts and labour. A straightforward flue clear or pressostat swap tends to sit towards the lower end of that range, while a fan motor replacement is typically £150–£300 depending on the specific model and your location (costs are generally higher in London and the South East). In rare cases where the PCB has been damaged by a prolonged fault, the bill can rise significantly — sometimes £350–£500 or more — but this is not the typical outcome.
Is the F.02 fault dangerous?
Yes, it should be taken seriously. The F.02 lockout exists specifically to prevent flue gases — including carbon monoxide — from being released into your home. The boiler shuts itself down as a protective measure, so while the lockout itself keeps you safe, the underlying fault must be resolved by a Gas Safe engineer before you use the boiler normally. If you experience any symptoms of carbon monoxide exposure (headaches, nausea, dizziness) evacuate the property, call 999, and then contact the National Gas Emergency Service on 0800 111 999.
Why does my Saunier Duval show F.02 only in cold weather?
Cold-weather F.02 faults are frequently caused by a frozen condensate pipe. When outdoor temperatures drop below zero, the condensate — a watery by-product of condensing boilers — can freeze inside the external section of the plastic pipe, creating a blockage that eventually disrupts the airflow monitoring circuit. Thawing the pipe with warm water and resetting the boiler usually clears the fault. If it keeps happening every winter, a Gas Safe engineer can re-route or insulate the condensate pipe to make it more frost-resistant.