BoilerFaultCodesYour boiler has experienced a power disruption while it was already trying to report a serious internal error, causing it to lock itself for safety.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Control fault: Voltage failure when malfunction causes interlock.
What causes this fault?
This fault occurs when the boiler experiences a sudden power cut or electrical surge at the exact moment it was trying to register a different internal error. This creates a conflict in the boiler's memory, as the control board cannot safely confirm why the system shut down. It is essentially a safety 'double-lock' that prevents the boiler from firing up until the electrical integrity of the control unit is verified.
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 0 4 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Remeha W40 60 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.