Ideal F6 fault codewhat it means and how to fix it
The outside sensor for weather compensation is reading wrongly or is not connected. It only appears on boilers that have one, or have been told they have one.
Take care
Get a Gas Safe registered engineer to look at your Ideal F6
We do not pass enquiries to a repair firm, so there is no form here. Find a Gas Safe registered engineer through the Gas Safe Register, and ask to see their registration card when they arrive — it is the register, not the van, that tells you they are qualified.
What F6 means
Ideal call this Outside Sensor Failure, and it belongs to the optional outdoor thermistor that lets a Logic or Vogue run weather compensation — lowering the flow temperature on mild days by reading the air outside. The sensor is a resistor screwed to a north-facing wall and wired back to the boiler's terminal block, and Ideal's chart expects it to read 31,000 to 35,000 ohms at 0°C, 15,000 to 16,500 at 15°C and 7,700 to 8,500 at 30°C.
Out of that range and the board reports F6. It is one of the few Ideal codes that can arise on a perfectly healthy boiler, because a sensor that was fitted, later disconnected and never told to the board leaves the board waiting for a reading that will never come. The boiler generally keeps heating, without compensation, while it shows the code.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Sensor wiring disturbed or corroded | The cable runs outside and into the terminal block behind the boiler cover, and Ideal's chart checks both ends for a secure connection before it condemns the sensor. | Common |
| Outside sensor failed | Sun, frost and a decade on a wall finish them. The published resistances give the test: a reading nowhere near 15,000 ohms on a fifteen-degree day is a dead sensor. | Common |
| Sensor removed but still enabled at the board | A previous engineer took it off, or a rewire lost the cable, and the board was never reconfigured. Nothing is broken; the setting is wrong. | Occasional |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£60–£180
Time on site
40 minutes
A visit to disable the input or reseat wiring £60–£90; a new outside sensor fitted £120–£180.
Typical UK prices including parts and labour, updated September 2026. Your quote may differ.
Own this appliance and had this code? . Nothing is published until a person has read it.
Related Ideal fault codes
- F4Get it checkedThe flow thermistor — the sensor reading the temperature of water leaving the heat exchanger — is giving a value the board will not accept. L4 is the same fault as a lockout.Related: sensors and thermistors
- F5Get it checkedThe return thermistor on the pipe bringing water back from the radiators is reading outside its range. On most Logic boards L5 is the locked-out form of the same fault.Related: sensors and thermistors
- L5Get it checkedTwo different faults share this code. On the two-window Logic ES boards it means five resets in fifteen minutes; on the 2011 Logic, the ESP1 and the Combi2 it is a return thermistor lockout.Related: sensors and thermistors
- FAGet it checkedThe return pipe is reading hotter than the flow, which cannot happen in a boiler that is plumbed and sensing correctly. Ideal call it a negative differential; the Vogue screen says Flow/Return Reversed.Related: sensors and thermistors
- F0Get it checkedOn the Logic Code Combi ES and first i-mini, F0 is the sensor that detects water flow reporting a fault. It is not the same as L3, which is the flow itself having stopped.Related: sensors and thermistors
- F0CGet it checkedThe hot water thermistor on a Logic Combi2 or i-mini2 is out of range. Heating usually carries on; the tap side suffers, because the board can no longer see the water it is making.Related: sensors and thermistors
Own an Ideal boiler? Save it and its codes come first next time.
Related guides
Common questions about Ideal F6
I do not have an outside sensor. Why am I seeing F6?
Because the board thinks you do. The compensation input is either wired or enabled, and if the sensor has been removed or a link disturbed the PCB waits for a resistance it never receives. An engineer either reinstates the sensor or switches the input off in the installer settings. Either is quick.
Will the boiler still heat the house with F6 showing?
Usually yes. Ideal list F6 as an F code, not a lockout, and the appliance falls back to running at the flow temperature set on the dial. What you lose is the efficiency of running cooler on mild days, which is worth having back but not worth a cold night.
Does this show on Vogue and Logic+ too?
Yes, in words: Outside Sensor Fault on the text screen, with Contact Installer beneath it. The 2011 Logic+ printed both spellings — Outside Sensor Fault on the screen and Outside Sensor Failure in the description column of its guide.
Technical review
Not reviewed by an engineer
No engineer has read this page. Severity follows what the manufacturer publishes, and we would rather tell you that than let a byline imply a sign-off.
Sources and how we verified this
We establish the facts from the sources below and then write the explanation ourselves. We do not copy manufacturer wording and we do not host their manuals.
- Manufacturer technical and service documentation
- Manufacturer support portal
This page has not been reviewed by an engineer, and we would rather tell you that than imply otherwise. The severity rating follows what the manufacturer publishes: where they say isolate the appliance and call someone, so do we.