How to clear hot water air lock?

I recently installed new hot and cold feeds to a new downstairs cloakroom. After refilling the system the hot taps were all dribbling, spluttering and showing signs of an air lock. I attached cold mains to a hot tap and left it running for 15 minutes, while opening up each hot tap. They all started flowing nicely and I had water flowing from the vent pipe into the hot water tank in the loft. Once I disconnected the cold mains feed though, the hot taps all dried up again. What should I try next please? For background, I have a pressurised central heating system and a Telford Copper Cylinders hot water cylinder on the same floor as the upstairs taps.

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