High
LED 4 on Ideal RD2

Your boiler is signalling an electrical wiring issue or a faulty thermostat connection, which is preventing it from communicating correctly to start your heating or hot water.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

What the manual says

Manufacturer manual

Application of power: Flash > 1/sec in sync with LED 3; Control 'stat open circuit or waiting for demand: On; Fan start up: Flash > 1/sec; Run: On; Pump over-run: Off; Lock-out: Off; Sensor Faults: Off; Reverse polarity: Flash > 1/sec alternately with LED 3.

From this model's manual
Verified against the Ideal Rd2 installation & service manual, page 38.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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