Boiler display shows E0 and unit will not fire; control appears unresponsive to thermostat call for heat.

Safety first: Turn off power to the boiler at the service switch and shut off the gas supply before removing any panels. Allow the boiler to cool.

• Step 1 – Power cycle: Turn off the boiler power for 2–3 minutes, then restore power. Check if the E0 code clears. If it returns, continue.
• Step 2 – Inspect low-voltage wiring: Remove the front access panel. Locate the low-voltage terminal strip on the control board (typically where thermostat and external controls connect). Check for loose, corroded, or broken wires. Tighten any loose screws and reseat plug-in connectors.
• Step 3 – Check external thermostat circuit: Disconnect the thermostat wires from the control (label them first). Install a temporary jumper between R and W (or T-T) terminals. Restore power and see if the boiler responds without the E0 code. If the code clears, the issue may be in the thermostat or field wiring.
• Step 4 – Inspect control board fuse: Many Bradford White boiler controls have a small low-voltage fuse. With power OFF, remove and visually inspect the fuse. Replace only with the same rating if blown. If it blows again, there is likely a short in the low-voltage circuit.
• Step 5 – Replace control board if needed: If wiring and fuse are good and E0 persists, the main control board is likely faulty and should be replaced by a qualified technician.

When to stop: If you smell burning, see scorched components, or the fuse repeatedly blows, stop and contact a licensed boiler technician.