Ideal F0t fault codewhat it means and how to fix it
A Logic Combi2 has lost contact with its room thermostat. Ideal's user guide says to check the thermostat's batteries; the installer manual adds its connections.
Take care
What F0t means
F 0t is Room Thermostat Fault, another code that first appears on the 2023 three-character Logic boards and their text-screen siblings. A boiler only knows to heat the house when the room thermostat closes a circuit or sends a signal, and this code is the board reporting that the thermostat input is not behaving — open when it should be closed, chattering, or a wireless receiver that has stopped hearing its transmitter.
Ideal give two levels of advice. The Logic+ user guide puts one line on the screen: check room thermostat batteries, which is right because a wireless stat with flat cells is by far the commonest way to lose the signal. The Combi2 installation manual says check the room stat and its connections, which is the engineer's version. It is the rare Ideal code where the fault is very likely not in the boiler at all, and where the fix may be two AA batteries.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Wireless thermostat batteries flat | Ideal's own first and only user-guide instruction. A receiver that has lost its transmitter reports nothing, and the board reports that. | Common |
| Thermostat wiring loose at the boiler terminals | The room stat connects at the terminal block behind the boiler cover. The installer manual's "check connections" covers a wire that has worked free or a receiver that has lost its supply. | Common |
| Thermostat or receiver failed | Room thermostats are not Ideal parts and fail on their own schedule. A stat that shows nothing on its own display has answered the question. | Occasional |
| Wireless pairing lost | A receiver that was unplugged, or a thermostat reset to factory, needs re-pairing to the receiver. The thermostat's own instructions cover it, not Ideal's. | Occasional |
What to try yourself
Change the batteries in the room thermostat, even if its display still shows something; a weak cell can run the screen and not the radio. This is Ideal's published step.
Turn the thermostat up above room temperature and listen for the click or watch for its heating symbol. If the boiler fires within a minute or two, the code will clear on its own.
If it persists, look at the thermostat's receiver — usually a small box near the boiler or the programmer — for a light. No light means no power to it, which is an electrician or installer job; a light and no boiler means pairing or wiring, which is the installer's.
Get a Gas Safe registered engineer to look at your Ideal F0t
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 it costs to fix
Typical repair cost
£0–£150
Time on site
15 minutes
Batteries, if that was it. A visit to reconnect or re-pair £60–£90; a replacement room thermostat fitted £80–£150.
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
- F9Get it checkedThe control board has not been told what boiler it is in, or has failed. L9 is the same fault locked out. The 2011 Logic Combi row also covers a gas valve short circuit.Related: electronics and power
- dUUsually simple to fixNot a fault. The diverter valve has been parked in its mid-position for servicing and the boiler is waiting to be told the service is over. Ideal publish the way out.Related: electronics and power
- Blank displayGet it checkedNothing on the screen at all. Ideal's user guides send you to the boiler's switch and the consumer unit first; the installer charts then work from the terminal block to the board.Related: electronics and power
- F7Get it checkedThe mains voltage reaching the boiler has dropped below what the board will run on. Ideal's advice is an electrician or your electricity supplier, not a heating engineer.Related: electronics and power
- C0Get it checkedThe board cannot activate the Boiler Chip Card that tells it what model it is fitted to. Ideal's engineer check is whether the small plastic card is in its slot at all.Related: electronics and power
- L9Get it checkedOn a Logic, L9 is the locked-out form of the unconfigured-board fault F9. On an Isar HE it is something else entirely: a heat exchanger overheat read by the dry-fire thermistor.Related: electronics and power
Own an Ideal boiler? Save it and its codes come first next time.
Related guides
Common questions about Ideal F0t
Can I still get hot water with F0t showing?
On a combi, yes: hot water does not go through the room thermostat. Heating will not run until the board sees a valid demand again. On a system or heat-only boiler, whether the cylinder still heats depends on how the controls were wired.
Does an older Logic show this?
No. The ESP1 and earlier boards have no room thermostat fault; a broken stat there just means the heating never comes on, with no code. F 0t belongs to the Logic Combi2, System2 and Heat2 and to the 2023 Logic+ and Logic Max as Room Thermostat Fault.
Is this Ideal's Halo thermostat?
It can be any thermostat wired to the terminals, including Ideal's Halo. The code is about the input, not the brand. If it is a Halo, its own app and manual cover pairing and batteries.
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
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.