Boiler will not start at all, no lights or display

Safety first: Do not open the boiler casing unless competent. Electrical work should be done by a qualified person.

User checks:

• Check the fused spur next to the boiler; ensure it is switched on and the fuse has not blown (typically 3A).
• Check the consumer unit for any tripped breakers and reset if safe to do so.
• Ensure any external controls (programmer, room stat) have power.

Engineer checks:

• Verify 230V supply at the boiler terminals.
• Check the internal fuse on the PCB (if fitted) and replace with the correct rating if blown.
• Inspect the boiler's on/off switch and wiring for continuity.
• Replace the PCB if it does not power up with a confirmed supply.

Restoring a safe and stable power supply is the first step before further diagnostics.