Error F6

Safety first

1. Do not attempt any gas-side work or remove safety covers unless you are a Gas Safe/registered installer. Isolate mains power to the boiler before accessing internal components. If you smell gas, evacuate and call the gas emergency number immediately.

Initial checks a homeowner can do

1. Note the exact display and symptom (F6 and any other lights). Press the boiler Restart button once as per the manual and observe whether the fault clears. If it clears and does not return, monitor the boiler for normal operation.

2. Power cycle the boiler: switch off at the mains isolator for 30 seconds and turn back on, then try Restart. This can clear transient electronic errors.

3. Check external controls: ensure the programmer/timer and room thermostat settings are correct and the mode knob is set to BOILER ON/appropriate position for heating so the boiler actually attempts to run. The outside sensor fault may only be reported when the boiler is calling for CH.

4. Visually inspect the outside sensor and its cable (only externally): locate the sensor on the outside of the property or near the eaves and check for obvious damage, disconnection, crushed cable, chewed wiring or severe corrosion. If the sensor or cable is dangling, visibly cut, or connectors are wet/oxidised, note that for the engineer. Do not pull on or force connectors.

Specific diagnostic steps and limited tests a competent homeowner might consider

1. If you are electrically competent and have a multimeter, with the boiler isolated at the mains you can trace the sensor cable from the outside sensor back to the boiler terminal (external inspection only). Check for physical breaks. Some outdoor sensors are simple NTC thermistors and will show a resistance value (e.g. several kiloohms at ambient temperature) — however exact values vary by sensor type, so do not attempt to replace parts based on a guessed value. If you are unsure how to interpret readings, stop and call an engineer.

2. Do not open the boiler casing or probe inside wiring or the PCB unless you are qualified. Opening the appliance may void warranty and is a gas safety risk.

3. If the outside sensor is detachable and dry, gently reseat any accessible external connector that you can access without removing the boiler cover. After reseating, restore power and try Restart.

When to call a professional

1. If F6 remains after reset and power cycling. 2. If you find damaged/chewed wiring, wet/corroded connectors, or the sensor is broken or missing. 3. If the boiler goes into lockout repeatedly or other fault codes appear. 4. If you are not confident performing the visual checks or any electrical continuity testing.

What the engineer will do (for your information)

1. A Gas Safe/registered engineer will isolate and safe the appliance, open the boiler if required, check sensor wiring at the PCB, measure sensor resistance and wiring continuity, inspect connectors for corrosion or water ingress, and either reterminate, repair or replace the outside sensor. If wiring and sensor test good they will check the control PCB and replace or reconfigure components if necessary.

Important final notes

1. Avoid trying to bypass or short the sensor to trick the boiler into running — that can disable safety features and create unsafe conditions. 2. If the boiler is under warranty or you are unsure, contacting the manufacturer or your installer is recommended. 3. If at any time you detect gas smell, leaks, or other urgent safety issues, stop and call the emergency services and a Gas Safe engineer immediately.