BoilerFaultCodesYour boiler's electronic brain has encountered a permanent memory error and has shut down the system as a safety precaution.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Controller - Non-volatile lockout
What causes this fault?
This fault occurs when the boiler's internal memory experiences a hardware failure, meaning it can no longer store or retrieve the vital settings needed to run safely. It is usually caused by wear and tear on the electrical components or a sudden power surge that has corrupted the main control board. Because the boiler can no longer trust its own safety instructions, it locks down permanently to prevent any operational risks.
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 404 — 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.