What it means
The Logic Combi2 shows it as F0U.
What to check, in order
- Turn the boiler off
Then let the radiators cool down.
- Bleed the radiators
Ideal suggests bleeding the radiators to release trapped air.
- Check the pressure
Ideal says the gauge should read between 1 and 1.5 bar. Top up if it's low.
- Turn the boiler back on
And see whether FU comes back.
When to call a Gas Safe engineer
If it returns, contact Ideal quoting FU, or a Gas Safe registered engineer: Ideal says it needs an engineer's visit.
Parts people end up buying
Only if the checks above point to a part. Match it to your model number first: it's on a label on the data badge, usually under the boiler or behind the front cover.
- Radiator bleed keySearch on Amazon
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Quick answers
What does the Ideal FU fault code mean?
The water coming back from the radiators is far colder than the water leaving the boiler, more than 50 degrees apart. Ideal says this points to a possible blockage. The Logic Combi2 shows it as F0U.
Can I fix Ideal FU myself?
Moderate (about 45 minutes). Start with: turn the boiler off; bleed the radiators; check the pressure. If it returns, contact Ideal quoting FU, or a Gas Safe registered engineer: Ideal says it needs an engineer's visit.
Is Ideal FU worth repairing?
Get a quote first. Bleeding and topping up are free. A blockage in the system needs an engineer, so ask for a price.
Checked against
- Ideal Heating: boiler fault codes, page 2
- Ideal Logic Combi2 installation and servicing manual, 04.2024 (PDF)
Last reviewed October 2026. Manufacturers update their pages, and your manual is the final word. Spotted a mistake? Email contact@appliance-error-codes.com.