F 0U High

Ideal F 0U Fault Code

Also written as F0U — same fault.

The Ideal F 0U fault code means: your boiler has detected that the water leaving it is much hotter than the water returning to it, meaning it cannot circulate heat through your home properly.. It appears on 5 Ideal models in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: Flow/Return Differential greater than 50 °C
Typical repair cost £150-300 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Ideal models that show the F 0U fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Ideal F 0U fault code information on this page is sourced and cross-checked against the official Ideal service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026