Halstead Ace 30 - No DHW - CH on using DHW taps?

4 year old Halstead Ace 30.
When turning the hot water taps on, 'H' shows on the display, swiftly followed by the dot to show boiler operating. However no hot water through the taps but CH gets hot (even though its switched off).
I'm assuming flow switch, is there anything I can flush out to possibly clean and loosen before calling in the professionals ?