greenstar heatslave 18/25 making a high pitched screech?

greenstar heatslave 18/25. We have disconnected a radiator and now the boiler is making a high pitched screech, I've bled the radiators, all fine, tried pressing the rest button but that does nothing so I'm obviously doing something wrong. I've turned the power off to the boiler as I'm a bit worried about it and now usnsure as to what to try ? I'm not brilliant with boilers (no knowledge at all, I've tried reading the instructins)so very basic instruction needed. This has happened before when we had a new bathroom fitted and the plumber fixed it straight away, I've rang him and he said uts just the reset button and wont tell me anymore as no doubt he'll want to come out for a callout fee for a ten second job... help !