BoilerFaultCodesYour boiler has detected a communication problem with your external thermostat or smart controls, meaning it cannot receive the command to turn on.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Wiring to external device error.
What causes this fault?
This fault occurs when the boiler loses its digital connection with your room thermostat or smart hub, preventing the message to 'turn on' from reaching the burner. The most common reasons are dead batteries in the wireless thermostat, a loose connection in the wiring behind the control box, or a faulty receiver component inside the boiler casing.
This fault is frequently reported in autumn when homeowners turn their heating back on for the first time and discover that thermostat batteries have drained over the summer.
DIY fix possible
Check if your wireless thermostat has run out of batteries and replace them.Ensure the thermostat receiver (usually near the boiler) is switched on and showing lights.Try resetting the boiler by turning the selector knob to 'R' for five seconds.Check if your internet router is on if you use smart controls like Hive or Nest.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like E.02 – .47 — 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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