Error F6

Safety precautions:

- Before doing any checks, turn the boiler off at the electrical isolation switch or the fuse spur. Allow the boiler to sit for a minute. Do not work on gas-carrying components. If you are unsure about any step, stop and call a Gas Safe registered engineer.

- If you need to open any electrical terminals or the boiler casing to inspect wires, only do so if you are competent with low-voltage electrical work. Isolate power first.

Initial checks a homeowner can do:

1. Reset the boiler: switch the boiler off at the fuse spur or isolation switch, wait 30–60 seconds, and switch it back on. Check if F6 clears. Many false codes are cleared by a reset.

2. Check any recent work: have you or an installer recently fitted or moved an outside sensor? If yes, contact the installer for a correct re-check of the installation.

3. Visual inspection of the external sensor and cable: locate the outside sensor on the exterior wall or where it was fitted. Look for obvious damage, crushed or cut cable, loose connectors, water ingress, or corrosion. If the sensor is dangling, severely corroded, or the cable is cut, do not attempt complex repairs yourself; call an engineer.

4. Check the connector at the boiler exterior: without opening the boiler cover, follow the cable route and check for damage visible outside the casing. If the cable disappears into the boiler casing you will need a competent person to open it.

Specific diagnostic and next steps (for competent DIY or to perform before calling an engineer):

1. If comfortable and competent with basic electrical checks, isolate mains power and remove the boiler casing to access the sensor connector on the PCB. Only do this if you know how to safely isolate power and reassemble the appliance.

2. Check that the sensor connector is fully seated on the PCB and that the cable is correctly wired with no loose pins. Re-seat the connector and replace the casing, restore power, and try a reset.

3. If you have a multimeter and the boiler manual lists expected sensor resistance values, with power isolated you can measure the sensor resistance across its two wires. Compare the measured resistance to the manufacturer’s expected value at ambient temperature. A very high or infinite resistance indicates an open circuit; a very low resistance suggests a short. If no manual is available, do not assume values—call an engineer.

4. If the sensor and wiring appear intact but the fault remains after reseating and resetting, suspect an internal PCB fault. At this point the problem is beyond usual homeowner repair.

When to call a professional:

- If the F6 code does not clear after a reset and simple external checks.

- If you find damaged cabling, corrosion, water ingress, or a disconnected sensor and you are not trained to replace the sensor or re-terminate wiring.

- If your checks show the sensor resistance is outside expected range or if reseating the connector does not help.

- If you are unable or unwilling to open the boiler casing or perform electrical checks safely.

- If the fault is intermittent, or you suspect the boiler’s PCB is at fault.

What to tell the engineer or installer:

- The boiler model and serial number, that it is showing F6, what you have already checked (reset done, visual inspection of sensor cable, any recent installation work). If the sensor was recently fitted or moved, say so.

Note: do not attempt gas adjustments, internal PCB repairs, or anything that affects the sealed combustion or gas components. Those tasks must be carried out by a Gas Safe registered engineer.