ER 20 High

Johnson Starley ER 20 Fault Code

Also written as ER20 — same fault.

The Johnson Starley ER 20 fault code means: your boiler's internal temperature sensor is failing to provide a reading, meaning the unit cannot safely manage its water temperature and has shut down to prevent damage.. It appears on 1 Johnson Starley model in our database.

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.

Technical description: Return plates probe fault
Typical repair cost £120-220 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Johnson Starley models that show the ER 20 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Johnson Starley ER 20 fault code information on this page is sourced and cross-checked against the official Johnson Starley service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026