Boiler shows E19; DHW flow is present but boiler does not switch to DHW mode

Safety first: Isolate electrical power and close the cold water inlet to the boiler before opening DHW components.

Steps to check:

• Clean inlet filter: Remove and clean the cold water inlet filter/strainer on the boiler to ensure adequate flow.
• Inspect DHW flow switch: Access the DHW flow switch or sensor assembly. Check for debris or scale preventing movement of the internal paddle or turbine.
• Check microswitch: On mechanical flow switches, verify that the microswitch actuates when flow is present. Replace if defective.
• Test operation: Reassemble, open the cold water supply, and run a hot tap. If the boiler still does not detect flow and E19 remains, the sensor may need replacement.

When to call a technician: If internal DHW components are heavily scaled, professional descaling or part replacement is recommended.