I have recently had central heating problems. The pump was replaced but since then the boiler is making kettling sounds. I have tried varying the speed of the new pump but this doesn't cure the problem or reduce the noise. Could this be caused by a build up of sludge or scale? If this is the case could it be flushed.
Sounds like air in the system as result of the pump change, if it has an auto air bleed it may be a simple case of turning on the filling loop until the pressure in the system reaches a stable presure of between 2-3 bar then turn off the filling loop. If the auto air bleed is working then the air will be removed by the addtional water.
If this doesnt cure it, I would suggest you invite your plumber back to complete the job they started.