Ideal F6 fault code: outside sensor fault
F6 means your boiler cannot get a valid reading from its outside temperature sensor, the weather-compensation probe fitted to an external wall. On its own, F6 does not stop your heating or hot water; it stops the boiler adjusting itself to the weather outside. Ideal's instruction is to reset once, then call an engineer. Here is what is safe to check first, and what the engineer will do when they arrive.
What does the Ideal F6 fault code mean?
Ideal F6 means your boiler cannot get a valid reading from its outside temperature sensor, the small weather-compensation probe fitted to an external wall. On its own it does not stop your heating or hot water. It is a control and efficiency fault, not a gas safety fault. Reset once, and if F6 returns, book an engineer.
Ideal's own installation and servicing manual for the Logic Combi ESP1 heads that section "'F6' - OUTSIDE SENSOR FAULT" (Section 4.10, page 59). Ideal's consumer fault-code page lists a flashing F and 6 as "Outside Sensor Fault" and tells you to "Reset the boiler. If this does not fix the problem, please contact us quoting error code F6 as this will require a visit from an engineer." The matching user guide calls the same fault "Outside Sensor Failure". Same fault, two wordings.
F6 does appear on Ideal's own public fault-code page, so you can check it against the manufacturer directly. It is a Logic ESP1 family code. Ideal's manuals confirm it on the Logic Combi ESP1 (24, 30 and 35kW) and the Logic Code Combi ESP1 (26, 33 and 38kW), the models with the small two-character display, and Ideal's general fault-code FAQ lists F6 across its domestic boiler range, so other boilers with that small display may show it too. The newer large-display boilers do not use the number at all: the Logic Max Combi2 (C24, C30, C35) manual and the Vogue Max Combi (26, 32, 40) manual both spell the same fault out in words as "OUTSIDE SENSOR FAULT", and neither document contains "F6" anywhere. The 2010 Logic+ Combi has no F6 either, because weather compensation was not offered on it.
F6 only appears on boilers that actually have an outside sensor fitted, and weather compensation is an optional extra rather than something every boiler has. What the code describes is the loss of that weather compensation, so the boiler can no longer trim its output to the temperature outside. You will feel that as a boiler running less efficiently, not as a boiler that has stopped.
F6 is not described as a combustion or gas safety fault by any of Ideal's documents. If you ever smell gas or your carbon monoxide alarm sounds, that is a separate emergency whatever is on the display. Call the National Gas Emergency Service on 0800 111 999 straight away and follow their instructions.
Key facts
The quick version, before the detail.
- What it means: the boiler cannot get a valid reading from its outside temperature sensor, the weather-compensation probe fitted to an external wall.
- Will it stop your heating? Not on its own. F6 costs you weather compensation, so the boiler runs less efficiently. You can carry on using your heating and hot water while you wait for an engineer, and switching the boiler off is safe too.
- DIY-fixable? Barely. Ideal's own instruction for F6 is to reset the boiler once, and you can look at the sensor from the ground. Everything past that needs the casing off.
- Engineer job if: F6 is still there after one reset. Ideal's manual gives every remaining step (testing the sensor, remaking the wiring, fitting a new sensor and replacing the PCB) to an engineer, not a homeowner. Ideal's instruction is to contact Ideal if the boiler is in warranty, or a Gas Safe registered engineer if it is not.
- Models: Ideal's manuals confirm F6 on the Logic Combi ESP1 (24/30/35kW) and Logic Code Combi ESP1 (26/33/38kW); other Ideal boilers with the small two-character display may also use it. The Logic Max Combi2 and Vogue Max Combi show the same fault as the words "OUTSIDE SENSOR FAULT" with no F number.
- Not a gas safety fault: none of Ideal's documents describe F6 as a combustion or gas safety fault. It sits on a sensor and control circuit.
- Smart Plan boiler and central heating cover is for future breakdowns, not a fault showing today, so book a one-off repair for the F6 you have now. Cover includes parts and labour up to £500 a year if your boiler is under 7 years old, or up to £200 a year if it is over 7. Those are annual limits shared across every fault in the 12-month period, so a bigger repair can cost more than the cover pays and you would pay the difference. Whether a specific part is covered depends on what the boiler and central heating module includes, which is set out in the plan terms. Smart Plan is a service plan, not insurance, cover is modular, and using a service starts a 12-month agreement period.
- Cover-plan call-outs are Monday to Friday, 08:00-18:00, unless it is a genuine emergency breakdown, and we aim to get an engineer out to you within two working days. One-off repair appointments run Monday to Friday, 09:00 to 17:00. A £95 call-out fee, paid in advance, applies in your first 30 days on a cover plan, for faults the plan does not cover, if the engineer cannot get access, and for early annual-service requests.
Why is my Ideal boiler showing F6?
F6 always points at the same short chain of parts: the outside sensor itself, the two wires running back to the boiler, and the board those wires land on. Ideal's manual works through them in that order, and so does the table below.
The order matters. An engineer starts by checking the wiring is securely connected at the boiler and at the outside sensor, then measures the sensor itself, then checks the wiring between the incoming terminal block and the printed circuit board. Replacing the board is the last step in Ideal's chart, not the first.
One clue worth giving the engineer before they arrive: whether anything happened just before the code appeared. Ideal's manual puts damage to the sensor down to weather, ladders or building work, so a storm, a new installation, decorating or a ladder against that wall are all worth mentioning. The sensor is only a small box on an outside wall with two thin wires.
Ideal F6 causes and who fixes them
| Likely cause | What you'll notice | Who fixes it |
|---|---|---|
| The outside sensor itself has failed | F6 shows and the boiler can no longer trim its output to the outside temperature, so the heating may run oddly. | Gas Safe registered engineer. Ideal's manual gives the sensor's expected resistance: 31,000 to 35,000 Ohms at 0C, 15,000 to 16,500 Ohms at 15C, and 7,700 to 8,500 Ohms at 30C. A reading outside those bands means the sensor is dead and must be replaced. |
| Loose, disconnected, corroded or broken wiring to the outside sensor | F6 appeared soon after a storm, a new installation, decorating or building work. | Gas Safe registered engineer. Ideal's first two checks are that the wiring is securely connected at the boiler and at the outside sensor. |
| Wiring between the boiler's incoming terminal block and the PCB is not secure | F6 shows even though the sensor tests fine and the outside wiring is sound. | Gas Safe registered engineer, with the front panel off. |
| The boiler's printed circuit board (PCB) has failed | F6 keeps coming back after the sensor and all the wiring have been proven good. | Gas Safe registered engineer. "Replace PCB" is the final step in Ideal's own fault-finding chart, not the first thing to try. |
| Physical damage to a sensor nobody knew was there | F6 on a boiler where you did not know an outside sensor existed. The box is often on a north-facing wall, and may be cracked, painted over, water-logged or knocked off. | You can safely look at it from the ground for obvious damage. Ideal's manual gives the replacement to a Gas Safe registered engineer, not to you. |
Can I fix an Ideal F6 fault myself?
Mostly no. Every diagnostic step in Ideal's manual for F6 needs the boiler casing off and a multimeter, so none of it is homeowner work. What you can safely do is reset once and gather information, which makes the engineer's visit shorter.
1. Reset the boiler once, exactly as Ideal's own fault-code page says. Press the restart button and give it a moment.
2. If F6 comes straight back, stop resetting. If you have already pressed it two or three times, no harm done, but stop there: five resets in 15 minutes puts the Logic into a separate LC lockout on top of the original fault.
3. Check the room thermostat and the programmer are switched on and calling for heat, so you can tell the engineer whether the heating works at all.
4. Read the pressure gauge on the boiler and note the figure. Normal cold pressure is 1 to 1.5 bar. F6 is not a pressure fault, but the reading is useful information for the engineer.
5. Look at the outside sensor from ground level. It is a small box on an external wall, often north-facing. Check for a cracked case, a cover knocked off, or a cable hanging loose or cut. Do not climb, and do not open it.
6. Check your other gas and electrical appliances are working normally, so you can tell the engineer whether the problem is only the boiler.
7. If the code is still there after one reset, call Ideal if the boiler is in warranty, or a Gas Safe registered engineer if it is not, quoting error code F6.
That is the whole safe list. Do not open the boiler casing, do not disconnect the sensor, and do not try to test it with a meter. Those steps sit in the installation and servicing manual for a reason: they are written for an engineer with the front panel off.
F6 is a control and efficiency fault rather than a combustion fault, so it is a booking rather than an emergency, and you can keep using your heating and hot water while you wait. If your heating or hot water has stopped as well, tell the engineer when you call, because that is extra information the code itself does not describe.
Is it F6, or one of the codes that look like it?
On the Logic's two-character display the F and the 6 flash alternately, which is why Ideal's own website writes it as a flashing F and 6. That flashing is also why F6 gets mixed up with its neighbours. Here is how they differ.
F5 is a return thermistor fault: reset once, then an engineer. L5 is the lockout variant of the same fault. On a small display a 5 and a 6 are easy to misread. Either way, the part involved is not on your outside wall.
L6 is a false flame lockout. An L on that display is commonly read or typed as an F, so an L6 often gets searched as F6. If the first character is an L, you are looking at a different fault entirely.
F7 is low mains voltage. Ideal's engineer chart says "LOW MAINS VOLTAGE - CONTACT ELECTRICITY PROVIDER", while its consumer page points you at a local electrician. Nothing to do with the outside sensor.
F4 is a flow thermistor fault, F3 is a fan fault, and F0 is a no water flow thermistor fault. All three follow the same pattern: reset once, then an engineer.
If what you are actually seeing is F1 or F2, those are the two most people expect. F1 is low water pressure and F2 is flame loss or ignition lockout. Both have their own pages with what to do about them, linked below. F8, F9, L8 and L9 all point at an unconfigured or faulty PCB.
One thing to ignore. Some listings pair F6 with the phrase "no CH operation but HW works OK". That is a separate troubleshooting section in Ideal's manual which happens to begin on the same page as F6. It is not what F6 means, and acting on it will send you looking for the wrong fault.
When should I call a Gas Safe registered engineer?
As soon as one reset has failed to clear it. That is Ideal's own instruction: reset the boiler, and if that does not fix the problem, contact them quoting error code F6, because it will require a visit from an engineer. Ideal's user guide puts it this way: contact Ideal if the boiler is under warranty, or a Gas Safe registered engineer if it is outside the warranty period.
Tell them the code, the model from the boiler's data badge, whether you know an outside sensor is fitted, and anything that happened just before the fault appeared. That list saves diagnostic time, because Ideal's manual gives four possible causes: the sensor, the wiring to it, the wiring between the terminal block and the board, and the board itself.
The engineer will disconnect the outside sensor and measure its resistance against Ideal's temperature table, check and remake the wiring at both the sensor and the boiler's terminal block, fit a new sensor if it reads wrong, and only replace the PCB once everything else has been proven good. You can check any engineer's registration on the Gas Safe Register before work starts.
If you ever smell gas, or your carbon monoxide alarm sounds, that is a separate emergency whatever code is on the display. Call the National Gas Emergency Service on 0800 111 999 straight away and follow their instructions.
Ideal F6 fault code FAQs
What does F6 mean on an Ideal boiler?
F6 means the boiler cannot get a valid reading from its outside temperature sensor. Ideal's installation and servicing manual for the Logic Combi ESP1 heads that section "'F6' - OUTSIDE SENSOR FAULT", and the matching user guide calls it "Outside Sensor Failure". The sensor is the small weather-compensation probe fitted to an external wall, so the boiler loses its ability to adjust its output to the weather. It is a control and efficiency fault, not a gas safety fault.
Can I fix an Ideal F6 fault myself?
Reset the boiler once, as Ideal instructs, then look at the outside sensor from ground level for obvious damage such as a cracked case or a loose cable. That is as far as it is safe to go. Testing the sensor's resistance, remaking its wiring and replacing the board all need the boiler casing off, so they are engineer work. If you have already pressed reset a few times, no harm done, but stop there: five resets in 15 minutes adds a separate LC lockout.
Why is my boiler showing F6 when I did not know it had an outside sensor?
Weather compensation is optional, so the sensor is easy to forget about. It is a small box on an external wall, often north-facing, wired back to the boiler with two thin cables. Ideal's manual puts damage down to weather, ladders or building work, so it can be painted over, cracked, water-logged or knocked without anyone noticing. F6 is often the first sign that it is there at all.
Will an F6 fault stop my heating and hot water?
No, not on its own. F6 sits on the outside sensor circuit, so what it describes is the loss of weather compensation rather than the loss of heat. The boiler runs less efficiently, but you can keep using your heating and hot water while you wait. Ideal's own instruction is a single reset, then a visit from an engineer. If your heating or hot water has also stopped, say so when you book, because that is extra information the code does not cover.
My Ideal boiler shows the words OUTSIDE SENSOR FAULT, not F6. Is that the same thing?
Yes. F6 is a Logic ESP1 family code, used on the models with the small two-character display. The newer large-display boilers show the same fault written out in words instead. The Logic Max Combi2 and Vogue Max Combi manuals both list it as OUTSIDE SENSOR FAULT with no F number, and the string F6 does not appear anywhere in either document. Those manuals set out the same checks and the same resistance table.
Is an Ideal F6 fault dangerous?
None of Ideal's documents describe F6 as a gas safety fault. It sits on the outside sensor circuit, which is about control and efficiency rather than combustion. You can carry on using your heating and hot water while you wait for an engineer, and switching the boiler off is safe too. If you ever smell gas or your carbon monoxide alarm sounds, that is a separate emergency: call the National Gas Emergency Service on 0800 111 999 straight away and follow their instructions.
What will the engineer actually do about F6?
They follow Ideal's own fault-finding order. First they check the wiring is securely connected at the boiler and at the outside sensor. Then they disconnect the sensor and measure its resistance: Ideal expects 31,000 to 35,000 Ohms at 0C, 15,000 to 16,500 Ohms at 15C, and 7,700 to 8,500 Ohms at 30C. A reading outside those bands means a new sensor. Replacing the PCB is the last resort.
Seeing F6 on your Ideal boiler? We can get an engineer out to you.
Book a one-off repair and a Gas Safe registered engineer will test the outside sensor, its wiring and the board, then tell you what needs replacing and what it will cost before any work starts. If a part has to be ordered in, that means a second visit. One-off repair appointments run Monday to Friday, 09:00 to 17:00, and one-off repairs do not carry a workmanship guarantee. Call 0333 772 6247 for the cost of a one-off repair before you book. Smart Plan is the other route. It is a service plan, not insurance, you build your own cover by picking only the modules you want, and you will see the exact monthly price for the modules you pick before you commit. A plan will not pay for the F6 you are looking at now, because cover is for future breakdowns, so for a fault you already have, a one-off repair is the thing to book. Before you sign up, here are the things that catch people out. Boiler and central heating cover includes parts and labour up to £500 a year if your boiler is under 7 years old, or up to £200 a year if it is over 7, and those are annual limits shared across every fault in the 12-month period, so a bigger repair can cost more than the cover pays and you would pay the difference. A £95 call-out fee, paid in advance, applies in your first 30 days, for faults the plan does not cover, if the engineer cannot get access, and for early annual-service requests. Using a module starts a 12-month agreement period from the first time you use a service, and leaving early after that costs the remaining months or 75% of the outstanding balance. There is a 14-day cooling-off period, which ends the moment a service is carried out. Cover-plan call-outs run Monday to Friday, 08:00-18:00, and outside those hours we attend only for a genuine emergency breakdown; we aim to get an engineer out to you within two working days. We are from UK Boiler Company Ltd, trading since 2014. Call 0333 772 6247.
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