ER 15 High

Johnson Starley ER 15 Fault Code

Also written as ER15 — same fault.

The Johnson Starley ER 15 fault code means: your boiler has detected that the water is getting much hotter than it should as it travels through the system, suggesting a blockage or a failure in how the water circulates.. 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: Differential over-temp across CH flow/return
Typical repair cost £150-350 (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 15 fault code

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

Source

Johnson Starley ER 15 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