I have an 18 rad system with an Ariston Boiler and unvented cylinder. Some of the radiators are barely warm and the system is inefficient and does not heat the whole house. The central heating has been extended onto an existing system along with a new boiler. for 3 years the system has struggled to heat the house and various plumbers/heating engineers have tried to improve things to no avail. I need an engineer to could recommend a fix for this system but they must be knwoledgeable about Ariston boilers. If you have the right kind of experience then please get in contact