BoilerFaultCodesGlow-worm Flexicom 18sx — Fault Code F42
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Coded resistance fault
What causes this fault?
This fault occurs when the boiler's main control board cannot identify the specific model it is installed in due to an incorrect or corrupted electrical resistance reading. The most common reason is a failure of the small coding resistor plugged into the board, or a communication error within the wiring harness. Without this data, the boiler shuts down as a safety precaution because it doesn't know its own operating parameters.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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A boiler cover plan would cover faults like F42 — no call-out fees, no surprises.
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Glow-worm Flexicom 18sx is discontinued — time for a new one?
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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