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Common domestic boiler faults include low system pressure, no ignition or a lockout, the boiler not firing for heating or hot water, and, in winter, a frozen condensate pipe. Modern boilers show a fault code on the display, which should be read against that manufacturer's manual, as the same code can mean different things.
Reviewed by Jordan Valentine-Dunn, Gas Safe registered engineer · Portsmouth Gas Heating · Last reviewed July 2026
Modern boilers are reliable, but a handful of faults come up again and again. Knowing the usual suspects helps you describe a problem accurately, though the fix for anything involving gas is a job for a Gas Safe registered engineer.
Most modern boilers show a fault or error code on the display. That code should always be read against that manufacturer's own manual, because the same code can mean different things on different boilers. A safety lockout should never be bypassed: many boiler faults, and any gas work, must be dealt with by a Gas Safe registered engineer.
Last reviewed July 2026. This guide is general information, not legal or safety advice, gas safety work must be carried out by an appropriately Gas Safe registered engineer. Rules can change, so check the linked official sources for the current position.