BoilerFaultCodesIdeal 4.8 Fault Code
Also written as 48 — same fault.
The Ideal 4.8 fault code means: your boiler has lost communication with the sensor that monitors the outdoor temperature, meaning it might not heat your home as efficiently as usual.. It appears on 8 Ideal models in our database.
Technical description: Outside Sensor Fault
What causes the Ideal 4.8 fault?
This fault occurs when the boiler can no longer detect a signal from the small sensor located on the outside of your property. The most common reasons are physical damage to the external unit from weather exposure or the electrical wiring becoming loose or corroded over time. Because the boiler doesn't know how cold it is outside, it can't automatically adjust its temperature to provide the most efficient heating.
This fault is often noticed during the first cold snaps of autumn or after heavy winter storms when wind or ice may have disturbed the external wiring.
DIY fix possible
Check the outdoor sensor for any obvious physical damage or loose wiresEnsure the sensor is not covered by snow, debris, or overgrown plantsReset the boiler to see if the fault clears
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Gas Safe Register →Ideal models that show the 4.8 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal 4.8 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