Saunier Duval F.32 Fault Code: Causes, Fixes & Repair Costs
What does the Saunier Duval F.32 fault code mean?
The F.32 fault code indicates that your Saunier Duval boiler has detected a problem with the combustion fan or flue gas evacuation. The fan is responsible for two critical jobs: drawing fresh air into the burner and pushing potentially dangerous flue gases safely out of your home. When the boiler's control board detects that the fan isn't running at the correct speed — or that there is insufficient draught through the flue — it locks out and displays F.32 as a safety precaution. Because poorly evacuated flue gases carry a real risk of carbon monoxide entering your home, the boiler will not restart until the underlying fault is resolved. If you see F.32, switch off the boiler, ventilate the room, and do not attempt to override the lockout.
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 external flue outlet — the pipe end visible on the outside wall or roof — can become blocked by bird nests, leaves, debris, or ice during a hard UK winter. Any obstruction creates back-pressure in the flue, reducing airflow to the point where the boiler's safety systems trigger F.32. This is statistically the most frequent cause of this fault on Saunier Duval boilers, and in many cases the fix is simply clearing the blockage.
- Faulty or Worn Combustion Fan Common
Over years of operation, the fan motor's bearings can deteriorate and its windings can burn out, causing the fan to spin too slowly or stop altogether. Vibration can also work electrical connections loose over time, meaning the control board never receives the signal confirming the fan is running — and locks out as a result. You may hear unusual grinding or rattling from the fan before it fails entirely.
- Defective Air Pressure Switch (APS) Common
The air pressure switch is a safety device wired between the fan and the control board. Its job is to confirm adequate draught before the boiler is allowed to ignite. If the switch itself develops a fault, it can send a false 'no draught' signal to the board even when the fan is spinning perfectly normally, producing an F.32 lockout with no actual fan problem. A Gas Safe engineer can test the switch with a manometer — it should activate at around 0.5–1.0 mbar.
- Kinked, Split, or Disconnected Pressure Sensing Tube Sometimes
A small flexible rubber tube connects the fan assembly to the air pressure switch. If this tube becomes kinked, pinched, cracked, or pulls free from its spigot, the pressure switch cannot sense the fan's draught correctly and will trip the F.32 code. This is a surprisingly common cause and one that a Gas Safe engineer can identify and rectify quickly, often at low cost.
- Frozen Condensate Pipe Sometimes
In cold UK winters, the external section of the condensate pipe can freeze solid. The resulting blockage causes a build-up of condensate within the boiler that disrupts airflow and can mimic the same pressure irregularities as a flue obstruction, triggering F.32. Thawing the condensate pipe is one of the few checks a homeowner can safely carry out themselves.
- Printed Circuit Board (PCB) Fault Rare
If the PCB itself is malfunctioning, it may misinterpret or fail to receive the signals sent by the fan or the air pressure switch, producing a spurious F.32 code even when both components are working correctly. PCB faults are relatively rare and are usually only diagnosed after all other causes have been ruled out by a Gas Safe engineer.
How to fix it
- Switch off the boiler and ventilate the room DIY safe
Because F.32 relates to flue gas evacuation, treat it seriously. Turn the boiler off at its controls, open a window or door in the boiler room, and allow a few minutes for any residual gases to clear before you carry out any checks.
- Check whether your condensate pipe is frozen DIY safe
In cold weather, locate the white plastic condensate pipe that exits your property — usually through an external wall and draining to a drain or gully. If it feels solid or looks iced over, thaw it gently using warm (not boiling) water poured along its length, or a hot-water bottle held against it. Never use a naked flame. Once thawed, try resetting the boiler.
- Visually inspect the external flue terminal for blockages DIY safe
From ground level (do not climb on ladders or onto roofs), use a torch to look at the flue outlet on the outside of your property. Check for obvious obstructions such as a bird nest, a build-up of leaves, or ice around the terminal. If you can safely see and reach a minor blockage from the ground, carefully remove it. Do not probe inside the flue itself.
- Reset the boiler — up to two or three attempts DIY safe
Turn the boiler off and wait five minutes for it to stabilise. Switch it back on, then press and hold the reset button (usually a red or black button on the front panel) for three to five seconds until the display clears. If F.32 returns immediately or after one heating cycle, do not keep resetting — repeated failed resets will not fix the underlying fault and can mask important diagnostic information for an engineer.
- Have a Gas Safe engineer inspect the pressure sensing tube and air pressure switch Gas Safe engineer
A registered engineer will check the small rubber tube that connects the fan to the air pressure switch for splits, kinks, or loose connections. They will also test the switch itself with a manometer to confirm it is opening and closing at the correct pressure threshold. Both the tube and the switch are relatively inexpensive to replace if found to be faulty.
- Have a Gas Safe engineer test and if necessary replace the combustion fan Gas Safe engineer
The engineer will electrically test the fan motor and check its speed against manufacturer specifications. If the bearings are worn, windings are damaged, or wiring is found to be loose or corroded, the fan will need to be replaced. Note that Saunier Duval no longer trades in the UK, so sourcing genuine or compatible parts may take longer than for current boiler brands — ask your engineer to confirm parts availability before proceeding.
- Have a Gas Safe engineer diagnose the PCB if all other components test satisfactory Gas Safe engineer
If the fan, APS, pressure tube, and flue all check out correctly, the control board itself may be at fault. PCB replacement is an expensive repair, and given that Saunier Duval boilers are now regarded as obsolete in the UK with limited parts availability, your engineer may advise that a new boiler represents better value than a costly PCB replacement. Ask for an honest assessment before committing to this repair.
Parts you may need
- Air Pressure Switch (APS) · from £52
- Combustion Fan / Fan Motor Assembly · from £145
- Pressure Sensing Tube (rubber connector) · from £12
- Flue Terminal Guard / Flue Terminal · from £25
- Printed Circuit Board (PCB) · from £320
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
Is F.32 dangerous — could it cause carbon monoxide poisoning?
F.32 is a safety lockout specifically designed to prevent the risk of carbon monoxide exposure. When the boiler detects that flue gases may not be evacuating correctly, it shuts itself down rather than continuing to run. As long as the boiler remains locked out and you do not attempt to bypass the safety system, the immediate risk is low. However, you should treat the fault seriously: switch off the boiler, ventilate the room, and arrange for a Gas Safe engineer to investigate promptly. If anyone in the property feels unwell, headachy, or dizzy, leave the building immediately and call the Gas Emergency line on 0800 111 999.
Can I fix F.32 myself without calling an engineer?
There are two checks a homeowner can safely carry out: thawing a frozen condensate pipe in cold weather, and visually inspecting the external flue terminal for obvious blockages reachable from ground level. You can also attempt one or two boiler resets. Beyond these steps, the fault involves the combustion fan, air pressure switch, and potentially the PCB — components that must only be worked on by a Gas Safe registered engineer. Do not attempt to open the boiler casing or interfere with any internal parts.
My Saunier Duval is quite old — is it worth repairing an F.32 fault or should I replace the boiler?
This is an important question for Saunier Duval owners because the brand no longer trades in the UK and its boilers are now considered obsolete. Parts can be harder to source and more expensive than for current brands such as Worcester Bosch or Vaillant. If the repair involves the air pressure switch or pressure tube, costs are relatively modest (typically £120–£250 all-in) and usually worth doing. If the engineer finds a failed fan, costs rise to around £250–£350, which may still be reasonable depending on the boiler's age. However, if a PCB replacement is required, the part alone can cost £300 or more — at that point, investing in a new boiler with a manufacturer warranty often makes better long-term financial sense. Always get at least two quotes and ask your engineer for an honest view.
How can I prevent F.32 from recurring?
Annual servicing by a Gas Safe engineer is the single most effective preventive measure — a proper service includes checking the fan speed, testing the air pressure switch, inspecting the flue, and catching deteriorating components before they cause a lockout. Additionally, fitting a flue terminal guard can reduce the risk of bird nests and debris blocking the outlet. In cold winters, lagging any exposed sections of the condensate pipe with pipe insulation helps prevent freezing. If F.32 is becoming a recurring fault even after repairs, this is a strong signal that the boiler is reaching the end of its serviceable life.