hot water air lock in pipes?

[horsegoesintoabar]

From a 2 year old combi boiler the hot water supply downstairs is working perfectly but no water from the hot taps upstairs. Cold supply fine throughout the house, the heating is fine to all radiators.

There's a slight noise from the boiler when the upstairs hot taps are opened. Could this be an airlock? If so, what's the best way to shift it?

Thanks!
Rog