Boiler completely dead – no lights or display, no response to controls.

Safety first: Before touching any wiring, ensure the boiler is isolated and verify absence of voltage with a suitable tester.

• Check external power: Confirm that the consumer unit breaker or fuse for the boiler circuit is on and not tripped. Reset if necessary, but investigate if it trips again.
• Inspect isolator switch: Verify that the boiler's local isolator is switched on and not damaged. Replace if it feels loose or overheats.
• Check boiler terminals: Remove the boiler's electrical cover and confirm that mains voltage is present at the input terminals when the isolator is on.
• Inspect internal fuses: Many Elnur boilers have internal fuses on the PCB or supply board. Check these with a multimeter and replace only with the same rating and type.
• PCB diagnosis: If power is present at the PCB but there is no display or response, the control board may have failed and require replacement.