BoilerFaultCodesYour boiler's main control unit is having a communication breakdown with its internal safety components, meaning it cannot operate safely and has shut down.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Internal fault: ISM not responding.
What causes this fault?
This fault occurs when the boiler's central brain loses its connection with the internal safety module that monitors the flame. The most common cause is an electronic failure within the internal circuitry or a loose connection on the main control board. Because the boiler can no longer verify that it is burning gas safely, it shuts down instantly as a protective measure.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
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A boiler cover plan would cover faults like Fault 02 / 100 — no call-out fees, no surprises.
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Could it be time for a new boiler?
If repair costs are adding up, a new energy-efficient boiler could be the smarter long-term choice.
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