Medium
F6 on Keston Combi C30

Your boiler is struggling to work out how hard it needs to fire because the sensor that monitors the outdoor temperature has stopped communicating correctly.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

What the manual says

Manufacturer manual

Outside Sensor Fault

From this model's manual
Verified against the Keston/Keston Combi C30 installation & service manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

Find a Gas Safe engineer
Search the official register →
Boiler cover options

Avoid the next call-out bill

A cover plan would handle faults like F6: no call-out fees, no surprise bills.

Approved partner
Domestic Appliance Guard
Unlimited call-outs, 24/7 helpline, no price-hike promise
Get a quote →

Affiliate links. We may earn a commission at no extra cost to you.

Related fault codes

F1View →F2View →L2View →

All 25 fault codes on the Combi C30

Seeing a different code? Every code this model can display, in one place.

F1F2F3F4F5Fan FaultFlame LossFlame On Before Gas OnFlow Thermistor FaultFlow/Return ReversedHigh Mains VoltageIgnition LockoutL1L2L6Low Mains VoltageOutside Sensor FaultOverheat LockoutPCB FaultReturn Thermistor FaultRoom Stat FaultSpare PCB Not SetToo Many RestartsWater Pressure

Related guides you might find useful

Yellow or orange flame — CO safety

Safety-critical — turn off, read this.

Read →

Is boiler cover worth it?

Break-even maths on monthly cover.

Read →

When to replace your boiler

7 signs repair isn't worth it anymore.

Read →