Blue light on, but boiler not operating during demand — No heat or hot water

What does Light on, no operation mean?

The blue indicator light is on, indicating power, but the boiler does not start heating when there is a demand for central heating or hot water.

• No active demand signal to the boiler from external controls
• An open bypass valve
• Issues with external controls like the diverter valve, frost thermostat, room thermostat, or programmer
• Faulty control board

Click steps to track your progress.

1. 1

   Ensure your central heating thermostat and hot water programmer are set to call for heat or hot water.

2. 2

   Check for any 'bypass' valves that might be open, diverting flow away from the heating system.

3. 3

   If only hot water or central heating is affected, confirm the respective external controls are operating correctly.

4. 4

   If the boiler still doesn't operate, contact a qualified service engineer to investigate.