Vibration in pipes

I have a pressurised system with a Worcester Bosch condensing boiler and Ariston unvented hot water tank. The central heating works fine but when we open the hot or cold taps (particularly both together when filling the bath or turning on the shower) there is a severe vibration through the pipes that lasts for about 5 seconds. The cold feed from the rising main is only 15mm and I am worried that this might be part of the problem although the incoming flow is adequate. The system was installed by a registered plumber so I assume that the expansion vessel and pressure valves are all OK. Any comments how I might solve this annoying noise.

check the taps first

Stupid question but what should I check them for?

going on your description the noise is only when you turn a tap on so the tap is the problem
the washer could be loose the guts may be vibrating when in use

Thanks a lot. I'll check them.

The tap washers are OK. The noise seems to come from the valve in the airing cupboard that is directly connected to the large accumulator!