Valiant atmotec pro?

I have a six month old hot water/central heating boiler.
I have a very noisy bubbling sound from the unit. A plumber turned down both water and heating controls. The proble is spasmodic but often returns. He told me it was calcium!!
I have a thremostat unit in my hallway and the radiator temperature heating will not come into effect with the temperature at 23 degrees if the system is turned down. If the controls are turned higher the wall thermostat operates the system.