Vaillant Boiler Fault Codes Explained: F22, F28, F75 and More
Vaillant ecotec boilers use a fault code system starting with the letter F to indicate the nature of a lockout or detected fault. London homeowners with a Vaillant boiler that has stopped working can use this guide to understand what the displayed fault code means, whether a reset is appropriate, and when an engineer is needed.
Understanding the Vaillant Fault Code System
Vaillant ecotec and ecofit boilers display fault codes on the digital display when the boiler detects a problem and initiates a lockout. The codes are prefixed with the letter F and are accompanied by a flashing flame symbol or a spanner symbol depending on the type of fault. Fault codes that indicate a safety lockout require a manual reset using the reset button before the boiler will attempt to restart. Fault codes that indicate a maintenance requirement or a component approaching the end of its service life may be displayed as advisory codes without causing a full lockout. The most frequently encountered Vaillant fault codes in London homes are F22, F28, and F75, each relating to a distinct system condition.
Vaillant produces several boiler ranges including the ecotec plus, ecotec pro, ecofit pure, and the older turbomax and thermocompact series. The F-code system is consistent across the modern ecotec and ecofit ranges. Older Vaillant boilers may display error codes differently, and the codes described here apply primarily to the current ecotec and ecofit product lines.
F22: Low Water Pressure Fault
The F22 fault code on a Vaillant boiler indicates that the system water pressure has fallen below the minimum operating threshold, typically 0.5 bar or below. Modern sealed central heating systems in London homes are designed to operate within a pressure range of approximately one to one point five bar when cold. If the pressure falls below this range, the boiler will display F22 and shut down to prevent running without adequate water circulation. The pressure gauge is located on the boiler casing and will show a reading below the normal operating zone, typically marked in green on the dial.
The F22 fault is often the first indication that the heating system has a slow water leak. In London properties, common sources of low pressure include a dripping radiator valve, a weeping pressure relief valve, a leaking towel rail connection, or a slow leak at a compression fitting under the floorboards. Before topping up the system pressure using the filling loop to restore it to the normal operating range, check for visible leaks at all accessible radiators and connections. If the pressure drops again within a few days of topping up, an engineer should be called to locate and repair the leak rather than continuing to add water, which dilutes the inhibitor in the system and accelerates corrosion.
F28 and F29: Ignition Fault Codes
The F28 fault code indicates that the boiler attempted to ignite and failed to detect a flame after the permitted number of attempts. The F29 code indicates that a flame was detected during the ignition sequence but extinguished shortly after the gas valve opened. Both codes result in a safety lockout requiring a manual reset. Common causes of F28 and F29 on Vaillant boilers include a dirty or failed flame sensing electrode, a blocked or sticking gas valve, low gas pressure, or a condensate drain blockage preventing normal operation in cold weather. In London during cold periods, a frozen condensate pipe is a common cause of the F28 fault and can be resolved without an engineer by following the thawing procedure described in the Vaillant user manual.
F75: Pressure Sensor or Pump Fault
The F75 fault code is one of the most frequently encountered on Vaillant ecotec boilers in London and indicates that the boiler detected no pressure differential across the pump when it attempted to start, which means the pump is either not running or the pressure sensor is not registering the flow. Common causes include a seized circulation pump, a failed pump capacitor, a blocked pump rotor, or a faulty pressure differential sensor. The F75 fault is more common on boilers installed in London hard water areas because limescale deposits can accumulate on the pump rotor over time and eventually cause it to seize. Prestige Engineers attend Vaillant F75 faults throughout London, typically resolving the issue by pump replacement, pump descaling, or pressure sensor replacement depending on which component has failed.