FU High

Ideal FU Fault Code

The Ideal FU fault code means: your boiler has detected that heat is building up too quickly and cannot circulate around your home, likely due to a blockage or a pump failure.. It appears on 15 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: DIFF GREATER THAN 50°C CHECK ISOLATION VALVES ARE OPEN CHECK PUMP CHECK RAD VALVES OPEN CHECK SYSTEM BLOCKAGES

What causes the Ideal FU fault?

This fault occurs when the temperature difference between the water leaving the boiler and the water returning to it becomes too high, usually because the water isn't moving fast enough. The most common reason is a failed internal pump or a physical blockage in the system, such as a build-up of sludge or closed radiator valves, which prevents heat from being carried away. Because the heat cannot escape, the boiler shuts down to protect its internal components from overheating.

This fault is more common in autumn when heating systems are switched back on after being idle all summer, which can cause pump seizing or debris to shift and create blockages.

Typical repair cost £150-£350 (including labour)

DIY fix possible

Check that the main isolation valves underneath the boiler are fully openEnsure at least two or three radiators have their valves turned to the maximum settingCheck that the boiler pressure is between 1.0 and 1.5 bar on the gauge

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Ideal models that show the FU fault code

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

Source

Ideal FU 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 27 April 2026