BoilerFaultCodesIdeal 4F Fault Code
The Ideal 4F fault code means: your boiler has reached an unsafely high temperature and has shut down to prevent damage or overheating.. It appears on 1 Ideal model in our database.
Technical description: Temperature safety sensor above 101 °C.
What causes the Ideal 4F fault?
This fault occurs when the water inside the heat exchanger becomes too hot, causing the safety sensors to shut the system down to prevent damage. The most common reasons are a failed pump that isn't moving water away from the boiler quickly enough or a blockage in the pipework restricting flow. It can also be caused by a build-up of air or a faulty sensor sending an incorrect temperature reading to the control board.
This issue is more common during the first cold spell of autumn, when pumps that have been idle all summer can seize up or struggle to restart.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Ideal models that show the 4F fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal 4F 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