Vokera Excell 96e?

Hi

Been having problems with this boiler over the last few weeks. The pressure gauge keeps dropping below the suggested 1.0 bar so I've been filling it up to between 1-1.5. The boiler works fine however the pressure either drops back after a day or so or on some occasions goes flying up until the release value opens. Also the low pressure and blocked flue light seem to flicker on intermittently and occasionally the hot water doesn't come own when the heating working. The situations is that when the boiler pressure gauge shows around 0.5 bar the boiler seems to be working fine. Been in the house nearly 4 years and haven't had it serviced yet. Assume that would be the first port of call?