"have managed to get pressure gauge to normal level as it does tend to drop frequently" - it shouldn't be doing that. Pressure is going SOMEWHERE
"bled my rads just incase they were upseting the boiler system. " - that may have dropped the pressure again; you'll be able to check properly with the system cold.
Did you register your boiler (Vokèra Linea One, Unica i, Mynute i or Vision boiler)? That'd have given you a 5 year warranty on the boiler instead of 12 months. - http://www.vokera.co.uk/homeowners/boiler-maintenance-2/register-boiler/register-5-year-product/
Dunno about other Vokèra boiler models.
Vokèra do offer fixed price repair:
That'll probably only be the boiler, so go round as much of the rest of the system as you can and eliminate that as a reason for losing system pressure thru a leak. Check for weeps and leaks at each pipework joint you can find, each rad valve, each drain off valve and each bleed valve.
There will also be a pipe that leads to the outside, which relieves overpressure in the system, via a pressure relief valve (PRV). Check this isn't weeping, which would suggest a problem with the pressure relief valve (Tie a plakkie bag over the end and see what collects).
If Vokèra are like Glow Worm, they may offer a 1 off fixed price call out (Beware: that may or may not include cover for the heat exchanger and the expansion vessel) and an alternative thru the likes of Domestic & General for a monthly fee. That MAY include the other items. The Glow worm offering was £299 for a fixed price one off callout or £50 a month for a minimum of 6 months for a service contract - Still £300 total and with service still provided by a Glow Worm engineer who has all the bits in his van. No contest really.
Plenty of Google search results that are for similar problems.
Some that may help: