F76 Boiler Fault Code: What It Means on Every Brand

The F76 fault code appears on 5 brands — Glow-worm, Heatline, Protherm, Ravenheat and Vaillant — and it does not mean the same thing on each. The same two or three characters can signal a pressure problem on one boiler and an ignition fault on another, so identify your brand first and use the table below to jump to the right page.

Up to: Stop & check now 5 brands use this code Meaning differs by brand

Which brand is your boiler?

The brand is printed on the front casing. Tap your brand for the full causes, fixes and repair costs.

Brand	What F76 means	Severity	DIY?
GWGlow-worm	The F76 code appears when the thermal fuse built into the primary heat exchanger has tripped. Full guide →	Lockout — engineer likely	No
HHeatline	The F76 code appears when the thermal fuse mounted on the primary heat exchanger has physically tripped due to dangerously high temperatures — typically above 95°C. Full guide →	Lockout — engineer likely	No
PProthermshown as F.76	The F.76 code appears when the boiler's thermal overheating protection triggers a safety shutdown on the primary heat exchanger. Full guide →	Stop & check now	No
RRavenheat	The F76 fault code on a Ravenheat boiler signals that the thermal fuse — a safety device mounted above the heat exchanger — has detected dangerously high temperatures and has cut power to… Full guide →	Stop & check now	No
VVaillantshown as F.76	The F.76 code appears on Vaillant ecoTEC Plus boilers when the thermal fuse mounted on the primary heat exchanger has physically tripped. Full guide →	Lockout — engineer likely	No

F76 brand by brand

Glow-worm F76

The F76 code appears when the thermal fuse built into the primary heat exchanger has tripped. This fuse sits at the top of the heat exchanger and acts as an emergency cut-out — when the heat exchanger reaches a dangerously high temperature, the fuse opens and the boiler locks out to protect itself from damage. The code can also appear if the wiring connecting that fuse to the PCB is broken or has a poor connection, meaning the boiler may not actually be overheating but is receiving a false signal indicating it is. Either way, the boiler will not restart until the underlying problem is diagnosed and resolved by a qualified engineer.

Causes, fixes & costs for Glow-worm F76 → · All Glow-worm codes

Heatline F76

The F76 code appears when the thermal fuse mounted on the primary heat exchanger has physically tripped due to dangerously high temperatures — typically above 95°C. Unlike a software lockout that can be cleared with a reset, this is a one-time-use safety device that permanently breaks the circuit once activated, bringing the boiler to a complete standstill. The boiler will not fire again until the fuse is replaced and the underlying cause resolved. Heatline boilers — including the Capriz, Advance, and Kalder ranges — share their core engineering with the wider Vaillant Group, so F76 carries exactly the same meaning and diagnostic pathway across all of these products.

Causes, fixes & costs for Heatline F76 → · All Heatline codes

Protherm F.76

The F.76 code appears when the boiler's thermal overheating protection triggers a safety shutdown on the primary heat exchanger. A dedicated thermal fuse, fitted at the top of the heat exchanger, trips automatically when temperatures climb beyond a safe threshold. Once tripped, the boiler locks out to prevent damage or a hazardous situation. Because Protherm shares its engineering platform and fault-code system with Vaillant (both are part of the same group), F.76 means exactly the same thing on both brands and is resolved in the same ways. This is one of the more serious faults a boiler can show: in some cases the heat exchanger itself has failed and the boiler may not be economical to repair.

Causes, fixes & costs for Protherm F.76 → · All Protherm codes

Ravenheat F76

The F76 fault code on a Ravenheat boiler signals that the thermal fuse — a safety device mounted above the heat exchanger — has detected dangerously high temperatures and has cut power to shut the boiler down. In plain terms, the boiler has overheated. The thermal fuse is designed specifically to protect the heat exchanger from damage, so when it trips and this code appears it means either the heat exchanger itself reached excessive temperatures, or one of the components responsible for monitoring and regulating heat has failed. This is a serious fault; the boiler will not fire again until the underlying cause has been identified and resolved by a qualified engineer. It is also worth noting that Ravenheat Manufacturing Limited was dissolved in 2025, following its parent company entering voluntary winding-up. Parts availability is becoming increasingly difficult, and many engineers are now advising replacement over repair for Ravenheat boilers displaying significant faults like F76.

Causes, fixes & costs for Ravenheat F76 → · All Ravenheat codes

Vaillant F.76

The F.76 code appears on Vaillant ecoTEC Plus boilers when the thermal fuse mounted on the primary heat exchanger has physically tripped. Unlike a software lockout that clears with a reset button, this is a one-time-use safety component that permanently breaks the electrical circuit the moment it detects dangerously high temperatures — typically above 95–105°C — inside the heat exchanger. Once tripped, the boiler will not operate again until the fuse is physically replaced by a Gas Safe registered engineer. Crucially, replacing the fuse alone is never sufficient; the underlying reason the heat exchanger reached those temperatures must also be identified and corrected to prevent an immediate repeat.

Causes, fixes & costs for Vaillant F.76 → · All Vaillant codes

Frequently asked questions

Is the F76 fault code the same on every boiler?

No. F76 means different things on different brands — see the table above. Always identify your boiler's brand (it is printed on the front casing) before acting on any advice about the code.

Can I fix a F76 fault myself?

Not usually. On every brand listed, F76 points to a fault that needs a suitably registered engineer to diagnose and repair. A single reset to rule out a transient glitch is reasonable; repeated resets are not.

Who should I call about a F76 fault?

For gas boilers, a Gas Safe registered engineer — it is a legal requirement for any work on the appliance. If you smell gas at any point, leave the property and call the National Gas Emergency line on 0800 111 999.

General guidance only — not a substitute for professional advice, and not certified by a registered engineer. Any work on a gas appliance must be carried out by a Gas Safe registered engineer. If you smell gas, call 0800 111 999.