dP Low

Johnson Starley dP Fault Code

Also written as DP — same fault.

The Johnson Starley dP fault code means: your boiler is currently running at its maximum power setting because a service mode used for testing has been activated.. It appears on 1 Johnson Starley model in our database.

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description: Maximum combustion rate (indicating sweep test mode)
Typical repair cost £0-90 (including labour)

DIY fix possible

Check if the 'Test' or 'Sweep' button has been pressed or held down accidentally.Turn the boiler power off at the fused spur switch, wait 30 seconds, and turn it back on to reset the electronics.Ensure the control dials are moved away from any maximum test positions.

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Johnson Starley models that show the dP fault code

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

Source

Johnson Starley dP 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 27 April 2026