Intergas Boiler Error Codes, Cause & How To Fix

Intergas Boiler Error Codes: Full Guide to Causes and Fixes 2026

Quick Answer: The most common Intergas boiler error codes are code 4 (no flame signal detected), code 9 (burner controller fault), code 11 (S1 sensor fault or circulation problem), and code 0.0 (low system pressure). Code 0.0 is the only fault most homeowners can resolve themselves by repressurising the system. All other Intergas fault codes require a Gas Safe registered engineer to diagnose and repair. Intergas Extreme and Exclusive models use a separate F-prefix code system covered in full in this guide.

Intergas is a Dutch boiler manufacturer that has built a growing reputation in the UK market for compact, reliable, and efficient gas boilers. Like all manufacturers, Intergas uses a fault code system to communicate problems on the control panel when something goes wrong. Understanding what each code means helps homeowners act quickly, avoid unnecessary call-out charges where a DIY fix is possible, and provide an accurate fault description to an engineer when professional help is needed.

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Intergas Boiler Error Codes: Standard Range

Code 0.0 — Low System Pressure

Code 0.0 is the most straightforward Intergas fault and the only one that most homeowners can resolve without a Gas Safe engineer. It indicates that the system water pressure has dropped below the minimum threshold required for safe and effective boiler operation. Low pressure is commonly caused by a small system leak, natural pressure loss over time, or a drop following recent radiator bleeding.

To restore pressure, locate the filling loop on the boiler and add water slowly to the system while watching the pressure gauge. The boiler manual confirms the correct target pressure for the specific Intergas model. Once the correct pressure is reached, close the filling loop firmly and attempt to restart the boiler. If pressure drops again shortly after being restored, a leak in the system is the likely cause and a Gas Safe engineer should locate and repair it.

Can you fix it yourself? Yes — repressurise via the filling loop to the manufacturer’s specified level. Call an engineer if pressure drops repeatedly.

Code 4 — Flame Signal Not Detected

Code 4 means the printed circuit board cannot detect a flame signal during or after the ignition sequence. The boiler will typically enter lockout mode when this code appears, preventing it from operating until the fault is identified and the boiler is reset. Before calling an engineer, the first check is to confirm the gas tap supplying the boiler is turned to the open position — an accidentally closed gas tap is a straightforward cause of code 4 that does not require professional help to resolve.

If the gas tap is open and code 4 persists after a reset attempt, a Gas Safe engineer should investigate. The most common component-level causes are a flame sensor that needs replacement, a faulty gas valve, a problem with the burner, or a fault within the PCB itself. The engineer should inspect all four before replacing any individual component.

Can you fix it yourself? Check the gas tap is open and attempt one reset. Call a Gas Safe engineer if code 4 persists.

Code 5 — Poor Flame Signal

Code 5 indicates the boiler is detecting a flame signal but it is too weak to confirm reliable ignition. This differs from code 4 where no signal is detected at all — code 5 points more specifically to a deteriorating flame sensor or ionisation electrode that is partially functioning rather than failed completely. A Gas Safe engineer should clean or replace the flame sensor and check the combustion quality before the boiler is returned to service.

Can you fix it yourself? No — a Gas Safe engineer is required.

Code 6 — Faulty Flame Detection

Code 6 indicates a fault within the flame detection system itself rather than a weak or absent signal. This can be caused by a failed ionisation electrode, wiring damage between the electrode and the PCB, or a PCB fault affecting the flame detection circuit. A Gas Safe engineer should inspect and test all components in the detection circuit before identifying which requires replacement.

Can you fix it yourself? No — a Gas Safe engineer is required.

Code 9 — Burner Controller Fault

Code 9 indicates an internal fault with the burner controller — the component that manages the ignition sequence, flame detection, and burner operation throughout the heating cycle. When this code appears it typically means the burner controller requires replacement rather than repair, as internal controller faults are rarely resolvable through adjustment or cleaning alone. A Gas Safe engineer should confirm the diagnosis before the replacement part is ordered.

Can you fix it yourself? No — a Gas Safe engineer is required.

Codes 10, 11, 12, 13, 14 — S1 Sensor Faults

These five codes all indicate a fault with the S1 sensor, which monitors the temperature of water in the central heating flow circuit. The specific code within the 10 to 14 range indicates the nature of the S1 fault — whether it is a complete failure, a short circuit, or an open circuit — and the different fault types require slightly different repair approaches. An engineer should check the sensor wiring before replacing the sensor itself, as a wiring fault can mimic a sensor failure and is an easier and less expensive fix.

Can you fix it yourself? No — a Gas Safe engineer is required.

Codes 20, 21, 22, 23, 24 — S2 Sensor Faults

These codes mirror the 10 to 14 range but relate to the S2 sensor — typically the domestic hot water or return temperature sensor depending on the specific Intergas model. The same diagnostic approach applies: the engineer should check wiring before replacing the sensor. A fault with the S2 sensor can affect hot water delivery performance and heating circuit management.

Can you fix it yourself? No — a Gas Safe engineer is required.

Code 0 — Faulty Sensor

Code 0 indicates a general sensor fault where the boiler’s control system has detected a problem with one of its monitoring sensors but cannot identify which specific sensor is responsible. A Gas Safe engineer should carry out a systematic inspection of all temperature and pressure sensors and their associated wiring to identify the faulty component.

Can you fix it yourself? No — a Gas Safe engineer is required.

Code 1 — High Temperature

Code 1 indicates the boiler has detected an abnormally high temperature within the heating system and has shut down as a safety precaution. The most common causes are a failing pump that is not circulating water effectively, a closed or partially closed radiator valve preventing circulation, or very low system pressure. A Gas Safe engineer should investigate the cause of the high temperature before the boiler is restarted, as repeated overheating can cause progressive and expensive damage to the heat exchanger.

Can you fix it yourself? No — a Gas Safe engineer is required.

Code 2 — Interchanged S1 and S2 Sensors

Code 2 is an unusual fault that indicates the S1 and S2 sensors have been connected to the wrong positions — most commonly following a recent repair or service where the sensors were disconnected and then reconnected incorrectly. An engineer should swap the sensor connections to their correct positions, which should clear the fault without any component replacement being necessary.

Can you fix it yourself? No — a Gas Safe engineer should correct the sensor connections.

Code 8 — Fan Speed Fault

Code 8 indicates the combustion fan is not running at the correct speed for safe operation. The fan controls the air supply to the burner and expels flue gases, and incorrect fan speed prevents the boiler from firing safely. Fan motor failure, a wiring fault, or a faulty fan control board are the most common causes. A Gas Safe engineer should inspect and replace the fan or associated components as required.

Can you fix it yourself? No — a Gas Safe engineer is required.

Code 27 — Outdoor Sensor Short Circuit

Code 27 indicates the outdoor temperature sensor has developed a short circuit. This sensor is used in weather-compensated heating systems to adjust the boiler’s output based on outdoor conditions. A short circuit in the sensor prevents accurate temperature reading. Sensor replacement by a Gas Safe engineer is required, though on some Intergas models the boiler may continue to operate in a default fixed-output mode until the repair is carried out.

Can you fix it yourself? No — a Gas Safe engineer is required.

Codes 29 and 30 — Gas Valve Relay Fault

These codes indicate a fault with the gas valve relay — the electrical component that controls the opening and closing of the gas valve in response to signals from the PCB. A faulty relay can prevent the gas valve from opening when heat is demanded or from closing when the boiler shuts down. Both scenarios require immediate inspection by a Gas Safe engineer, as a relay fault affecting gas valve operation is a potential safety concern.

Can you fix it yourself? No — a Gas Safe engineer is required.

Full Intergas Standard Error Code Reference

Intergas Extreme and Exclusive Error Codes

The Intergas Extreme and Exclusive boiler ranges use a separate F-prefix fault code system that differs from the standard range. These codes provide more detailed fault descriptions across a wider range of components.

F-Code Reference Table

Key F-Code Explanations

F000 — Heat Exchanger Sensor Replacement Required. This code indicates the heat exchanger sensor has reached the end of its serviceable life and requires proactive replacement. It is more of a service reminder than an active fault, but should be acted upon promptly to prevent a heat exchanger overtemperature event.

F001 and F002 — High Temperature During Operation. These codes indicate overheating during central heating and hot water modes respectively. The distinction helps an engineer identify whether the overheat is occurring in the primary heating circuit or the domestic hot water circuit, which narrows the likely cause. Poor circulation, closed valves, and low pressure are the most common causes of both.

F003 — High Flue Gas Temperature. Excessively high flue gas temperatures can indicate a heat exchanger problem, incomplete combustion, or a flue restriction. The boiler should not be restarted until the cause is confirmed by an engineer.

F018 — Blocked Flue or Air Supply Duct. A blocked flue or air supply duct prevents safe combustion and flue gas expulsion. Checking that the external flue terminal is not physically blocked by debris or ice is a practical homeowner check before calling an engineer, as a physically clear flue terminal can sometimes be confirmed without professional help.

F028 — Reset Error. This code, similar to the Navien E787, indicates a problem during the reset process. Attempting the reset sequence again from the beginning will often clear F028 without any further action. If it persists after a second reset, a Gas Safe engineer should investigate.

FAQ

What does Intergas error code 4 mean?

Intergas error code 4 means the printed circuit board cannot detect a flame signal, causing the boiler to enter lockout mode. The first check before calling an engineer is to confirm the gas tap supplying the boiler is in the open position, as an accidentally closed tap is a simple cause that does not require professional help. If the gas supply is confirmed and a single reset does not clear the fault, a Gas Safe engineer should inspect the flame sensor, gas valve, burner, and PCB to identify the specific cause.

Can I fix Intergas boiler faults myself?

Code 0.0 — low system pressure — is the only standard Intergas fault code that most homeowners can resolve themselves, by repressurising the system via the filling loop. Checking the gas tap before calling an engineer for code 4, and checking the external flue terminal for physical blockages for F018, are also practical homeowner steps. All other Intergas fault codes require a Gas Safe registered engineer to diagnose and repair safely.

What is the difference between standard Intergas codes and F codes?

Standard Intergas error codes — shown as single or double digit numbers — apply to the core Intergas boiler range including the Combi Compact and HRE models. F-prefix codes apply specifically to the Intergas Extreme and Exclusive boiler ranges and provide more detailed fault descriptions across a broader range of components. If the code on the boiler display includes an F prefix, the Extreme/Exclusive code table in this guide is the correct reference. Both code systems require a Gas Safe engineer for the vast majority of faults.

What does Intergas code 9 mean?

Intergas error code 9 indicates an internal fault with the burner controller — the component that manages the full ignition and combustion cycle. When code 9 appears it typically means the burner controller requires replacement, as internal controller faults are rarely resolvable through adjustment alone. A Gas Safe engineer should confirm the diagnosis before the replacement part is ordered and fitted.

What causes Intergas error codes 10 to 14?

Intergas error codes 10 to 14 all relate to faults with the S1 sensor — the temperature sensor that monitors the central heating flow circuit. The specific code within the range indicates whether the fault is a complete sensor failure, a short circuit, or an open circuit in the sensor wiring. A Gas Safe engineer should check the sensor wiring before replacing the sensor itself, as a wiring fault can produce the same code as a failed sensor and is typically less expensive to repair.

How do I prevent Intergas boiler fault codes?

Annual servicing by a Gas Safe registered engineer is the most effective way to prevent Intergas fault codes. During a service the engineer cleans the burner and flame detection components, checks gas pressure and combustion quality, inspects the flue and air supply, tests all sensors and their wiring, and identifies components approaching the end of their serviceable life. Many of the most common Intergas codes — including 4, 5, 6, and 9 — are directly preventable through regular professional maintenance. Keeping the system pressure within the correct range also prevents code 0.0 from appearing.

When should I replace an Intergas boiler rather than repair it?

An Intergas boiler under 10 years old with a single fault is almost always worth repairing. For boilers over 10 to 12 years old where multiple fault codes are recurring or where major components such as the PCB, burner controller, or heat exchanger require replacement, the economics of continued repair versus a new A-rated installation are worth reviewing honestly with a Gas Safe engineer. A new boiler will typically deliver better efficiency and lower running costs from the day of installation, and the cumulative saving from improved efficiency can offset the replacement cost over the subsequent decade.

Conclusion

Intergas boilers use a clear and well-structured fault code system across both their standard and Extreme/Exclusive ranges, with the F-prefix codes on the premium models providing more granular fault detail that helps engineers diagnose problems efficiently. Of all the codes covered in this guide, code 0.0 is the only one most homeowners can resolve independently — by repressurising the system via the filling loop. Checking the gas tap for code 4 and confirming the external flue terminal is clear for F018 are also practical first steps before calling an engineer.

For all other fault codes, a Gas Safe registered engineer is the right call. Annual servicing remains the most effective prevention strategy for Intergas boilers, keeping the flame detection system, sensors, and combustion components clean and correctly calibrated throughout the boiler’s expected 10 to 15-year operational lifespan.