Boiler displays F0 and will not start heating or providing hot water

Safety first: Turn off the boiler using the main power switch and isolate it from the electrical supply. Close the gas valve. Allow the boiler to cool completely before removing any covers. Only Gas Safe / certified technicians should work on gas-carrying components.

Steps to check the flow NTC sensor:

• Remove the front panel to access the hydraulic group and flow pipe leaving the heat exchanger. Locate the flow NTC sensor (usually clipped into a pocket on the flow pipe with two low‑voltage wires leading to the PCB).
• Visually inspect the sensor and wiring for damage, corrosion, or signs of overheating. Ensure the connector is firmly seated on both the sensor and the PCB.
• With power still isolated, disconnect the NTC and measure its resistance using a multimeter. Compare the reading to Protherm’s NTC resistance chart (typically around 10 kΩ at 25°C, but check the service manual for the exact value). If the reading is open circuit, shorted, or far outside tolerance, the sensor is faulty.
• If the sensor tests bad, replace it with a genuine Protherm flow NTC sensor. Apply a small amount of thermal paste if specified and ensure it is fully inserted into the pocket.
• If the sensor tests OK, check continuity of the wiring harness from the sensor plug to the PCB plug. Repair or replace the harness if any conductor is open or shorted.
• If both sensor and wiring are good, the fault may be on the main PCB. Inspect for burnt tracks or components. Replacement of the PCB should be done by a qualified technician and followed by all required configuration steps.

After repair: Reassemble the boiler, restore power and gas, reset the boiler, and run a heating demand to confirm that the F0 code has cleared and the flow temperature is being read correctly.