BoilerFaultCodesYour boiler has shut down because a remote safety device or clever external control has sent a signal to stop the system from running.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: External interlock activated
What causes this fault?
This fault occurs when an external safety device or control unit intentionally breaks the electrical circuit to stop the boiler from firing. The most common reason is a faulty zone valve that has failed to open or an external frost thermostat that has triggered to protect the pipework.
This code is more frequent during extreme cold spells if an external frost thermostat is installed or if a zone valve motor seizes after being inactive through the summer.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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