BoilerFaultCodesYour boiler's main internal computer or its configuration module has developed a communication failure, preventing the system from operating safely.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Control box or the heat control module (HCM) is defective – HCM or control box connections need to be checked
What causes this fault?
This fault occurs when the boiler's main control board loses communication with the small memory chip that stores its specific operating settings. The most common reason is a physical connection failure or a component failure on the circuit board, which prevents the boiler from knowing how to safely manage the burner.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
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A boiler cover plan would cover faults like F1259 — no call-out fees, no surprises.
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Parts for discontinued models can be hard to find and expensive. A new A-rated boiler could save you money on both repairs and energy bills.
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