What to do
- Reset the boiler
Press the restart button.
When to call a Gas Safe engineer
If the code comes back, contact Ideal quoting F4 (or L4): it needs an engineer visit. Outside the warranty, use a Gas Safe registered engineer.
A repair visit will usually check the sensor's reading and its wiring.
Before you book
- Note the model and serial number. They're on a label on the data badge, usually under the boiler or behind the front cover.
- Write down the exact code, and what the appliance was doing when it appeared.
- Check whether it's still under warranty. If it is, the repair may cost you nothing.
Checked against
- Ideal Heating: what does my boiler fault code mean
- Ideal Heating: Logic Combi 24, 30 and 35 troubleshooting guide
- Ideal Heating: boiler fault codes, page 2
Last reviewed September 2026. Manufacturers update their pages, and your manual is the final word.