High
21 on Johnson Starley Reno HE

Your boiler's internal computer is struggling to read data from its sensors, which prevents it from safely controlling the heat.

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

ADC error

From this model's manual
Verified against the Johnson Starley Bm Johnson Starley Amp Johnson Reno Starley He16h He25h He31h He16hp He25hp He31hp installation & service manual, page 24.
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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