Worcester Greenstar 30i ERP - Low HW Flow at Taps

[NEWT1116]

Any advice gratefully received on this problem.

I have a Worcester GS 30i ERP with quoted DHW of 11 lpm but only delivering max 8.5 to 9 lpm at hot taps and shower on full flow through 15mm pipework with no flow regulators in taps.
CW inlet to boiler is 19 lpm 3bar/43psi restricted down to 11 lpm through flow regulator on input to plate HE. I have a pressure regulator fitted to incoming mains set to 3bar.
Boiler flow turbine and regulator are clear of any debris so no issues with flow into plate HE. Boiler flow turbine reading (1.1d) shows DHW 8.9 lpm on full flow.

I've established through temp differential tests the following:
- Cold water inlet temp 10.8 deg - HW outlet temp 44.8 deg at full flow measured at sink tap near boiler showing a DT of 34 deg
- HW return temp measured at return to pump pipe (from diverter) 34.7 deg on full flow
- HW remains at constant temp at tap on full flow and boiler doesn't cycle
- Temp readings suggest that the plate HE is converting heat 1-1 from primary side to secondary so not suggesting any blockage in the plate HE.

Am I optimistic in expecting 11 lpm at the taps or does this symptom suggest a blockage or fault elsewhere?

[wine~o]

What flow rate do you get at the cold on the kitchen tap ?