Our flat has a Volkera Compact 25 HE boiler which is kettling occasionally (I don't know quite how oocasionally yet).
It was installed five years or so ago and has been serviced (and passed its gas safety tests) but probably hasn't had a 'major' service.
The installer suggests that the system needs a 'power flush' at quite considerable cost. Is this really likely to be the cure and/or necessary or should we be looking at other things first?