What the F3 code means
Every modern Ideal boiler has a fan that pushes air through the burner and carries the waste gases out through the flue. Before the boiler lights, and all the time it is running, the control board checks a speed signal coming back from the fan. If that signal is missing, too low or does not match what the board asked for, the boiler cannot be sure the flue gases are being cleared safely. It shuts down and shows F3.
On most Logic, Logic+ and Logic Combi2 models, as well as related ranges such as Logic Max and Vogue, F3 is listed simply as a fan fault. It is a safety shutdown rather than a sign that anything dangerous has happened. The boiler is refusing to run until it knows the fan is doing its job.
Occasionally F3 is a one-off, for example after a brief power dip, and a restart clears it for good. If it keeps returning, something inside the boiler needs attention.
Common causes of F3
A worn or failing fan
The fan runs every time the boiler fires, so after several years the bearings can wear. A fan on its way out often gets noisier first, with a whine, rattle or rumble when the boiler starts. Eventually it slows down or stops, and the boiler reports F3.
Loose or damaged wiring
The fan is connected to the main control board by a power lead and a signal lead. Ideal's servicing instructions ask engineers to check that these connections are secure at both ends and that the wiring has not deteriorated. A loose plug or a damaged wire can cut the speed signal even when the fan itself is fine.
Control board (PCB) fault
If the fan and wiring test correctly, the board that drives the fan and reads its signal may be at fault. This is less common, but an engineer will rule it out before replacing parts.
Electrical supply problems
A power cut or a dip in the mains supply while the boiler is running can interrupt the fan and trigger F3. This type usually clears with a restart and does not come back.
Something restricting the air or flue
A blocked air intake or flue can make the fan work outside its normal range. This is rarer, and checking it means working on the flue, which is strictly an engineer job.
| Cause | Typical sign | Who fixes it |
|---|---|---|
| Power dip or cut | F3 appears once and clears after a restart | You, by restarting the boiler |
| Worn fan bearings | Whining or rattling noise before the fault | Gas Safe engineer |
| Loose or damaged fan wiring | Fault comes and goes, no noise | Gas Safe engineer |
| Control board fault | Fan and wiring test fine but F3 persists | Gas Safe engineer |
| Flue or air intake restriction | Fault under load, sometimes in windy weather | Gas Safe engineer |
Safe checks you can do yourself
There is no homeowner repair for a fan fault, but a few simple checks can clear a one-off F3 and give your engineer useful information.
- Check the power. Make sure the fused spur that feeds the boiler is switched on and that nothing else in the house has lost power.
- Restart the boiler. Press reset as your manual describes, or switch the boiler off at the fused spur, wait a minute and switch it back on.
- Give it a few minutes. Let the boiler run through its start-up sequence before deciding whether the restart has worked.
- Listen as it starts. Make a note of any grinding, whining or rattling from inside the casing, as this points towards the fan.
- Stop after two or three attempts. Repeated resets will not fix a worn fan, and on some models too many restarts in a short time trigger a separate LC lockout.
Do not remove the boiler casing or try to reach the fan. The fan sits in the sealed combustion section of the boiler, and any work there must be done by a Gas Safe registered engineer.
When to call a Gas Safe engineer
Book a Gas Safe registered engineer if F3 returns after two or three restarts, if the boiler has been noisy for a while, or if the fault keeps appearing a few times a week. The engineer will test the fan, check the wiring and connections, and look at the control board and flue if needed.
When you call, give the exact code, the model name from the front of the boiler and a description of any noise. Engineers who work on Ideal boilers often carry common Logic parts, so good information can mean the fix is done in one visit.
If your boiler is still within its manufacturer's warranty, contact Ideal or your installer first, as a fan replacement may be covered.
Typical repair costs in the UK
If a restart clears the fault for good, it costs nothing. If a part is needed, these are the typical ranges we see, including parts and labour. Prices vary by region, model and engineer, so treat them as a guide.
| Job | Typical UK cost |
|---|---|
| Engineer call-out and diagnosis | Typically £80 to £150 |
| Remaking or repairing fan wiring | Typically £80 to £150 |
| Fan replacement, fitted | Typically £180 to £350 |
| Replacement PCB | Typically £300 to £550 |
| Flue repair or adjustment | Typically £100 to £300 |
How to stop F3 coming back
A fan wears gradually, so the best protection is a yearly service. During a service an engineer checks the combustion readings and listens to the fan, which often shows wear before it becomes a breakdown. Our boiler service cost guide explains what is included. Do not ignore a boiler that has started to whine or rattle on start-up, as that is often the early warning. If your boiler also struggles to light, have a look at our page on the Ideal L2 ignition lockout, and see the Ideal fault code hub for the other codes we cover.