What it means
On the Logic Combi2 it shows as F 05, or L 05 when the boiler has locked out. One entry in Ideal's FAQ describes L5 as too many resets instead, so if you see L5, check your user guide.
What to do
- Reset the boiler once
Press the restart button and see whether the code comes back.
When to call a Gas Safe engineer
Ideal says F5 needs a visit from an engineer. Contact Ideal quoting F5 if the boiler is under warranty, or a Gas Safe registered engineer if not.
A repair visit will usually check the sensor's reading and its wiring.
- 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.
Quick answers
What does the Ideal F5 fault code mean?
There's a fault with the return thermistor, the temperature sensor on the water coming back from the radiators. On the Logic Combi2 it shows as F 05, or L 05 when the boiler has locked out. One entry in Ideal's FAQ describes L5 as too many resets instead, so if you see L5, check your user guide.
Can I fix Ideal F5 myself?
Engineer only (engineer visit). Start with: reset the boiler once. Ideal says F5 needs a visit from an engineer. Contact Ideal quoting F5 if the boiler is under warranty, or a Gas Safe registered engineer if not.
Is Ideal F5 worth repairing?
Worth fixing. A thermistor is a routine part for an engineer to replace.
Checked against
- Ideal Heating: what does my boiler fault code mean
- Ideal Logic Combi2 installation and servicing manual, 04.2024 (PDF)
- Ideal Heating: boiler faults FAQs
Last reviewed October 2026. Manufacturers update their pages, and your manual is the final word. Spotted a mistake? Email contact@appliance-error-codes.com.