What the F9 code means
The printed circuit board, or PCB, is the brain of the boiler. It reads the sensors, controls the fan, pump and gas valve, and decides when it is safe to light the burner. Each board has to be set up for the exact boiler it is fitted to, because the same type of board is used across several models and outputs. That set-up is called configuration.
F9 tells you the board is not happy with its own set-up or its own electronics. In Ideal's user guide for the older Logic Combi ESP1 models, F9 or L9 is listed as an unconfigured PCB. In the guides and installation manuals for later models, including the Logic Combi2 and Logic Max ranges, the description is wider: unconfigured or faulty PCB, or a gas valve short circuit. As usual with Ideal, the F version is a fault and the L version is a lockout.
You may see F9 or L9 described elsewhere as a pressure or overheat fault. Ideal's own manuals do not describe it that way for the Logic family, so we go by the manufacturer's wording here.
Common causes of F9
A new or replacement board that has not been configured
This is the classic cause. If an engineer has recently fitted a new PCB, it needs configuring for your boiler model before it will run. If that step was missed or not completed, the boiler shows F9 or L9 straight away.
A fault on the control board
Boards can fail through age, heat or damage. A power surge, a lightning strike nearby or water getting onto the electronics can all cause a board to lose its settings or develop a fault.
Gas valve short circuit
On models where Ideal includes it in the description, an electrical short in the gas valve or its wiring can also trigger this code. The board detects the fault and refuses to operate the valve.
Wiring or connection problems
Loose or damaged connections between the board and other components can sometimes produce the code, particularly after other work has been carried out on the boiler.
| Cause | Typical sign | Who fixes it |
|---|---|---|
| New PCB not configured | Code appears right after a board was replaced | The engineer who fitted it |
| Faulty PCB | Code after a power cut, surge or leak | Gas Safe engineer |
| Gas valve short circuit | Code returns straight after a restart | Gas Safe engineer |
| Wiring or connection fault | Code after other repairs on the boiler | Gas Safe engineer |
Safe checks you can do yourself
There is very little a homeowner can do about a board fault, but these steps are safe and worth trying before you pay for a call-out.
- Think about recent work. If the boiler has just had a new PCB fitted, contact the engineer who fitted it first, as the board almost certainly needs configuring and the job is not finished.
- Check the power. Make sure the fused spur is on and that there are no tripped switches on your consumer unit.
- Restart once. Switch the boiler off at the fused spur, wait a minute or two and switch it back on. Some electrical glitches clear this way.
- Look for water. Without opening the casing, check under the boiler for drips, as water on the electronics can cause board faults.
- Do not keep resetting. If the code returns after two or three attempts, leave the boiler off and book an engineer.
Never open the boiler casing or touch the PCB or gas valve. The board carries mains voltage and the gas valve controls the gas supply to the burner. Both are strictly for a Gas Safe registered engineer. If you smell gas at any point, turn off the supply at the meter if it is safe to do so and call the National Gas Emergency Service on 0800 111 999.
When to call a Gas Safe engineer
If F9 or L9 does not clear after a single power restart, you need a Gas Safe registered engineer. They will check the board's configuration, test the gas valve and its wiring for a short, and look for signs of damage or water. Sometimes the fix is simply configuring the board correctly, which is quick. If the board or gas valve has failed, it will need replacing.
If the fault appeared after another engineer replaced the board, ask them to come back first. Configuring the board is part of fitting it, so you should not normally pay again for that step. If your boiler is under warranty, contact Ideal or your installer before booking anyone else.
Typical repair costs in the UK
These are typical ranges including parts and labour. Board prices vary a lot between models, so ask for a quote before work starts.
| Job | Typical UK cost |
|---|---|
| Engineer call-out and diagnosis | Typically £80 to £150 |
| Configuring an existing board | Typically £80 to £150 |
| Replacement PCB | Typically £300 to £550 |
| Replacement gas valve | Typically £250 to £450 |
| Earthing or wiring fault | Typically £80 to £200 |
How to stop F9 coming back
Board faults are hard to prevent completely, but a few habits help. Have leaks near the boiler fixed quickly, because water and electronics do not mix. Our guide on a boiler leaking water explains what to look for. Make sure any replacement board is fitted and configured by a Gas Safe registered engineer using the correct part for your model. A yearly service lets an engineer spot scorched connections or corrosion early, and our boiler service cost guide covers what is included. For other Ideal codes, see the Ideal fault code hub.