Error F.10

Safety first:

1. If the boiler shows F.10, switch the boiler off at the programmer/room thermostat and use the boiler’s main on/off switch. If you are unsure, turn the boiler off at the isolator and turn off the mains electricity before doing any physical checks. Do not attempt to work on gas components or carry out flue/combustion adjustments. If you smell gas, leave the property and call your gas emergency service immediately.

2. If you are not comfortable working with electrical appliances or removing the boiler casing, stop and contact a Gas Safe registered engineer. Do not attempt gas-related repairs.

Initial homeowner checks (non-invasive):

1. Reset the boiler using the reset procedure in the user manual or the control knob. Note if the error clears and whether it returns immediately or after some time. Record how often it occurs.

2. Check for obvious signs of external water leaks around the boiler, especially near pipework where the flow sensor sits. Water ingress into connectors can cause short circuits.

3. Visually inspect any accessible external wiring to the boiler (e.g., thermostat wires, external controls) for damage, chewing, or loose connections. Make sure external controls and room thermostats are correctly set.

4. Check the boiler pressure gauge and general status lights — while F.10 is a sensor short, unrelated system faults (very low pressure, pump problems) can mask or trigger other errors. Do not try to repressurise the system if you are unsure; read the manual or call a pro.

If you are competent with basic electrical checks and have isolated the boiler power (CAUTION: only proceed if safe and confident):

1. Remove the boiler casing following the manufacturer instructions (power isolated). Locate the flow NTC sensor—typically mounted on the flow pipe or heat-exchanger and connected to the PCB by a two-wire connector.

2. Check the sensor connector for corrosion, moisture, melted insulation, or loose pins. Dry and reseat the connector if damp. If the connector/wiring looks damaged, do not operate the boiler; arrange a service visit.

3. With the sensor still connected to the wiring harness, use a multimeter to check for a short to earth/ground: measure resistance between each sensor wire and the boiler chassis or earth. A healthy sensor wiring should not show near-zero ohms to earth. If you read near zero ohms to earth, there is likely a short in the wiring or sensor.

4. Unplug the sensor from the harness and measure resistance across the two sensor wires. A short circuit will show a very low resistance (near zero). An open circuit will show infinite/very high resistance. (Note: do not rely on specific resistance values unless you have the exact sensor specification; the important checks are: not shorted to earth, not open, and not zero ohms.)

5. If the sensor appears shorted or open, replacing the flow NTC is commonly the fix. If the sensor checks OK (reasonable resistance, not shorted to earth), inspect the wiring harness for damage and the PCB connector for burnt or loose pins.

When to call a professional:

1. If the error persists after reseating connectors, drying any moisture, and resetting the boiler, call a Gas Safe registered engineer. If the sensor or wiring is faulty, a qualified engineer should replace the NTC, repair wiring, and test the system.

2. If you find signs of wiring damage, burnt connectors, or suspect a PCB fault you must get a professional. PCB-level diagnostics and component replacements must be done by a trained technician.

3. If you are asked to remove the boiler casing but are not trained, stop and call a professional — working inside the boiler risks electric shock, gas risks and invalidation of warranties.

Notes and final advice:

1. Do not attempt any gas valve, burner, flue or combustion adjustments yourself. Those tasks are for Gas Safe engineers only.

2. Keep a record of when the fault occurs, any reset attempts, and any visible conditions (damp, intermittent fault after rain, power cuts). This information helps the engineer diagnose intermittent wiring or moisture-related issues.

3. Replacing a faulty flow NTC or repairing wiring commonly fixes F.10. If replacing sensors does not cure the fault, further electronic diagnosis by a professional will be required to check the wiring loom and PCB.

4. For safety and compliance, use a Gas Safe registered engineer (or equivalent in your country) for all repairs involving gas, combustion, or internal boiler wiring.