BoilerFaultCodesIdeal 20 Fault Code
The Ideal 20 fault code means: your boiler has stopped working because it cannot properly measure the temperature of the water coming back into the system.. It appears on 1 Ideal model in our database.
Technical description: Return sensor is defective or not properly connected.
What causes the Ideal 20 fault?
This fault occurs when the boiler's internal computer loses communication with the sensor that monitors water temperature returning from your radiators. The most common reason is that the sensor has physically failed due to age or internal wear, though it can also be caused by loose or damaged wiring. Because the boiler cannot accurately track the system temperature, it shuts down as a safety precaution to prevent overheating.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Ideal models that show the 20 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal 20 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