BoilerFaultCodesYour boiler has experienced a direct failure of its main internal computer brain and cannot control the heating or hot water safely.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Internal failure - electronic
What causes this fault?
This fault occurs when the boiler's internal computer chips or circuits suffer a physical breakdown, meaning the unit can no longer process data or send signals to parts like the pump or gas valve. The most common reason is general component fatigue over time, though it can also be triggered by a sudden electrical surge or moisture getting onto the control board.
This fault is slightly more common during winter or periods of heavy rain, as increased humidity or high electrical demand on the local grid can put extra stress on ageing electronic components.
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 →Protect yourself from future repair bills
A boiler cover plan would cover faults like 406 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Ideal Response SE is discontinued — time for a new one?
Parts for discontinued models can be hard to find and expensive. A new A-rated boiler could save you money on both repairs and energy bills.
Affiliate links — we may earn a commission at no extra cost to you.