My gas heating system is powering up, the pressure is ok, but there is a mad ticking coming from the downstairs radiator, and none of the radiators are working properly. Some arent working at all, others have a little heat at the top. Ive tried increasing the pressure, and I have bleed all of the radiators, but still no heat. Its a new house, and Ive lived here for 6 months. Is the builder liable to fix this? Any ideas what the fault is?