Ideal H F fault codewhat it means and how to fix it
The flame detection electrode on an Isar, Icos, Mexico HE or Esprit has failed Ideal's continuity test — a short circuit, in the Icos wording. The electrode is replaced, or the board.
Take care
Get a Gas Safe registered engineer to look at your Ideal H F
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 H F means
H F is Flame Detection Error in its temporary form, and it is not L F. L F is the lockout after three failed ignitions; H F is the board reporting that the flame detection circuit itself is wrong before or between attempts, which the Icos manual spells out as Flame Detection — Short Circuit Error. The detection electrode is the probe that sits in the flame and carries the tiny ionisation current that proves the burner is alight. If that probe or its lead is shorted to earth, or the board's input has failed, the boiler can never prove a flame and will not try.
Ideal's chart is two questions long: remove the flame detection electrode terminal from the PCB and check for continuity between the two terminal pins — if there is continuity, replace the flame detection electrode; if there is not, replace the PCB. The Logic family has no direct equivalent; a detection electrode fault on a Logic surfaces as a failed ignition, L2, rather than as its own code, which makes H F the more helpful message of the two for an engineer.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Detection electrode shorted or cracked | The ceramic insulator on the probe cracks with heat cycling and the lead earths to the casing. Ideal's continuity test finds it directly. | Common |
| Lead chafed or terminal corroded | The electrode lead runs beside the burner. A lead that has cooked, or a terminal that has corroded in condensate, reads the same as a failed probe. | Occasional |
| PCB flame-sensing input | No continuity at the electrode, and H F still showing: Ideal's chart replaces the board. | Rare |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£80–£380
Time on site
40 minutes
A flame detection electrode £80–£150 fitted. A PCB, if the electrode passes Ideal's test, £200–£380.
Typical UK prices including parts and labour, updated September 2026. Your quote may differ.
Parts you may need
We may earn a commission if you buy a part through one of these links. It does not change what you pay, and it does not affect which parts we list.
Ideal Logic ignition electrode
175565£18–£42Authorised Ideal parts distributor
Price checked 28 September 2026
Ideal Logic primary PCB
£150–£320Authorised Ideal parts distributor
Price checked 28 September 2026
Own this appliance and had this code? . Nothing is published until a person has read it.
Related Ideal fault codes
- L2Stop — call an engineerThe boiler failed to detect a flame during ignition and has locked out on the gas valve. Do not keep resetting it.Related: ignition and gas supply
- F2Get it checkedThe flame was lost during operation. Ideal direct you to check the gas supply first, and that is genuinely the right order.Related: ignition and gas supply
- LCUsually simple to fixYou have reset the appliance five times in fifteen minutes. This is not a fault in itself — it is the boiler asking you to stop.Related: ignition and gas supply
- L FStop — call an engineerAn Isar, Icos, Mexico HE or Esprit has made three attempts to light and locked out; the LED window flashes L then F. Ideal permit one reset and a gas supply check, then an engineer.Related: ignition and gas supply
- L6Stop — call an engineerA flame is being detected when there should not be one. Turn the appliance off and call a Gas Safe engineer rather than resetting it.Related: ignition and gas supply
- F16Stop — call an engineerThe board has detected a fault in the gas valve or its wiring. Nothing here is for a householder to try; Ideal's checks cover the valve's supply and coil and end with replacing it.Related: ignition and gas supply
Own an Ideal boiler? Save it and its codes come first next time.
Related guides
Common questions about Ideal H F
What is the difference between H F and L F?
L F is the ignition lockout: three attempts, no flame proved, boiler latched off until reset. H F is the flame detection circuit itself reporting a fault, usually a shorted electrode. One is a result, the other is a component telling you why.
Will it clear by itself?
H codes can, and an intermittent short — a lead touching the casing only when hot — produces an H F that comes and goes. It is not a code that fixes itself, only one that hides for a while.
Is this the electrode that gets changed at a service?
On these boilers the ignition and detection electrodes are separate parts, and Ideal's chart for H F concerns the detection one. It is a routine replacement and a modest bill.
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.