BoilerFaultCodesIdeal 4A Fault Code
The Ideal 4A fault code means: your boiler has shut down because a sensor has detected that the water inside is getting too hot.. It appears on 1 Ideal model in our database.
Technical description: Temperature supply sensor too high (> 101 °C).
What causes the Ideal 4A fault?
This fault occurs because the water leaving the boiler has exceeded a safe temperature limit, causing the system to shut down for safety. It is usually caused by a lack of water flow, often due to a pump failure or a blockage within the heat exchanger that prevents heat from being carried away quickly enough. In some cases, the sensor itself may simply be faulty and providing an incorrect high-temperature reading.
This issue is more frequent during the first cold spell of autumn, when pumps that have sat idle all summer can seize up upon restarting.
DIY fix possible
Check that all radiator valves are fully open to allow water to circulateCheck that your system pressure is between 1.0 and 1.5 bar on the gaugeOnce the boiler has cooled down, try to reset the unit
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Gas Safe Register →Ideal models that show the 4A fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal 4A 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