Boiler displays F.01 and shuts down, no heating or hot water

Safety: Switch off electrical supply and isolate gas before opening the boiler casing. Only competent persons should remove the combustion cover.

• Reset and observe: Reset the boiler using the front panel reset button. If F.01 reappears quickly, proceed with checks.
• Visual inspection: Locate the flow NTC on the flow pipe. Check for signs of leaks from the primary heat exchanger or pipe joints dripping onto the sensor or connector. Dry any moisture and correct leaks.
• Check wiring: With power off, unplug the sensor and inspect the connector pins for corrosion or bridging. Inspect the cable for crushed or melted insulation that could cause a short to another conductor or to earth.
• Measure resistance: Test the NTC with a multimeter. A reading near 0Ω indicates a shorted sensor; replace the flow NTC if so.
• PCB inspection: If the sensor and wiring are sound, the PCB input may be shorted internally. Look for burn marks or damaged components on the PCB. Replacement of the PCB should be done by a qualified engineer.