Boilermate 2 keeps filling up

Hello all

Any advice appreciated , my Boilermate 2 appears to be functioning correctly very hot water etc, however in the last couple of days noticed 2 strange things

1) every 5 mins or so a gurgling sound (like large bubble of water rising to the top of the tank)
2) every 5 mins or so the system seems to start filling up for a couple of seconds , but can’t find any leaks anywhere so don’t know where the water is going

Any ideas ?

Plus what’s the best way of finding a plumber that would b capable of servicing it (the last one we got to have a look when we moved in 2 years ago couldn’t work out how it worked), should I look for something particular ?

Thanks
Toby

Google up for your area.
Check ball valve in the top tank.
Does the water overflow to outside.

Could be blockage some where.
Check / bleed rads
Could be internal coil which is mains water has a hole.
Would be game over then.

Mike