BoilerFaultCodesIdeal 40 Fault Code
The Ideal 40 fault code means: your boiler has lost its electrical power supply or there is a fault with the incoming electricity to the unit.. It appears on 1 Ideal model in our database.
Technical description: Check the mains supply.
What causes the Ideal 40 fault?
This fault occurs when the boiler's control system detects a total loss of incoming electrical power. The most common reason is a blown fuse on the circuit board or a tripped switch at the main fuse box, though it can also be caused by a faulty wall switch or a failure in the boiler's internal wiring.
This fault is occasionally more frequent during the winter months when power surges or local grid instability are more likely due to heavy electrical demand and adverse weather.
DIY fix possible
Check if other appliances in the house have powerCheck your home's consumer unit (fuse box) to see if a circuit breaker has trippedEnsure the boiler's isolation switch (usually located near the boiler) is turned onCheck if your pre-payment meter (if applicable) has credit
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Search the official register for a qualified engineer in your area.
Gas Safe Register →Ideal models that show the 40 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Ideal 40 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