Ideal Thermal Fuse Lockout
A Vogue has stopped because the one-shot thermal fuse on its heat exchanger reads open circuit. Ideal allow one reset; if the message returns, the fuse has usually blown and the heat exchanger is replaced.
Take care
Get a Gas Safe registered engineer to look at your Ideal boiler
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 this means
Every Vogue — the 2013 original, the Gen2 and the Max — carries a thermal fuse on the heat exchanger that no Logic has. It is a last line behind the overheat thermistors: a one-shot link that opens permanently if the casting reaches a temperature the sensors and the software should never have allowed. The board watches it through a connector on the primary PCB, an 8-way plug on the Gen2 and Max and a 6-way on the first Vogue, and Thermal Fuse Lockout means that circuit is open.
Ideal's fault-finding sequence is short and entirely electrical. Isolate the supply; make sure the two-way connection to the fuse is pushed fully home and the multi-way plug is properly seated on the PCB; press RESTART and power cycle; if the message persists, check continuity across the black and yellow wires in pins 1 and 2 of the connector, then across the fuse itself.
A fuse with no continuity means a new heat exchanger — Ideal do not offer the fuse as a separate cure — while a fuse that reads fine sends the engineer to the wiring or the primary PCB. The first Vogue's screen offered the householder "Reset Boiler, if fault persists contact installer", which is as far as anyone without a meter should go.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Heat exchanger genuinely overheated | Circulation failed — a pump that stopped, a system run dry, valves shut — and the casting cooked before the thermistors could hold it. The fuse opened as designed and will not close again. | Common |
| Fuse connector not pushed home | Ideal put this first in their chart. The two-way plug on the fuse and the eight-way plug on the board both come off during a service, and a plug left proud reads exactly like a blown fuse. | Common |
| Wiring or primary PCB fault | Continuity across the fuse but no continuity at the board pins means the loom; continuity at both and a message that persists means the board. Both are at the end of Ideal's sequence for a reason. | Occasional |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£70–£1,100
Time on site
30 minutes
A connector re-seated is a short visit, £70–£110. A primary PCB £250–£380 fitted. A heat exchanger on a Vogue is the expensive outcome, typically £600–£1,100 fitted, and worth a warranty check before anyone pays for it.
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.
Central heating circulating pump
CH-PUMP-15-60£90–£180Plumbing merchant
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
- L1Get it checkedThe boiler is not seeing enough water flow through it to run safely, so it has stopped. Usually a pump, an air lock, or a blocked filter.Related: overheat and circulation
- FDGet it checkedNo water flow has been detected. The pump is the prime suspect and this will become an overheat if it is left.Related: overheat and circulation
- L3Get it checkedThe boiler has stopped because it cannot detect water moving through it. Ideal's own steps are to fill the system to 1 bar with it cold, bleed the radiators and try again.Related: overheat and circulation
- L AGet it checkedThe overheat thermostat on an Isar, Icos, Mexico HE or Esprit has tripped and the boiler has locked out. Ideal say hold reset for two seconds; if it recurs, switch off and call the installer.Related: overheat and circulation
- FUGet it checkedThe water leaving the boiler is more than 50°C hotter than the water coming back, which means very little of it is moving. Check the valves are open before anyone condemns the pump.Related: overheat and circulation
- F12Get it checkedThe pump rotor is jammed. Ideal's remedy is to clear the blockage — on a modern Logic that is an engineer freeing or replacing a sealed pump head, not a screwdriver in a bleed screw.Related: overheat and circulation
Own an Ideal boiler? Save it and its codes come first next time.
Related guides
Common questions
Why replace the whole heat exchanger for a fuse?
Because that is Ideal's published remedy. Their chart goes from "no continuity across the fuse" straight to "replace the heat exchanger", and a fuse that has opened means the exchanger has been hotter than it was ever meant to be, so it is not a component anyone should want to keep in service anyway.
Is it the same as Overheat Lockout?
No. Overheat Lockout comes from the flow thermistor reading too high and clears with a reset once things cool down. The thermal fuse sits behind that protection and does not reset; if it has opened, the overheat protection was passed.
Does a Logic have a thermal fuse?
Not one that reports. The message appears in the Vogue installation manuals and in none of the Logic, Logic+ or Logic Max manuals read for these pages.
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.