Blue light Slow flash (off then on) — Central heating not working (hot water OK)

What does Blue light Slow flash (off then on) mean?

The blue indicator light flashes slowly (briefly turning on from an off state), and the central heating system is not operating, though hot water may still be available. This suggests an issue with central heating demand.

• Problem with the external diverter valve
• External timer or room thermostat issue
• Temperature control set to frost protection position
• Unintended live demand at ST10-LR from another source

Click steps to track your progress.

1. 1

   Check the external timer or room thermostat settings to ensure there is a demand for central heating.

2. 2

   Verify the boiler's temperature control is not set in the frost protection position.

3. 3

   If an external diverter valve is fitted, ensure it is functioning correctly and not stuck.

4. 4

   If the problem persists, an installer should check for unintended live signals at ST10-LR.