I think its because of the failure, as phishfood mentioned. There is also the fact that the air pressure must be balanced and the air admittance valves are only activated by negative pressure. So if there is too much positive pressure, they will not help, but they can be used in conjunction with Positive Air Pressure Attenuator.
My guess is that there were too many failures because people installed inferior quality parts. Allegedly they are supposed to last 20 or 30 years.
Yes.. It's true.. But we make this job also as service for other plumbers.. They call us, we make a videoinspection,we clean it, but if there are need to dig, change the pipes,this work will make by the plumber that has called us..
Hi mate! The Grey parts are those who here we call "malta".. It is a mix of lime, concrete, sand and water.. The copper, it is heating.. It's an old type of heating that in italy was use much years ago called " monotubo".. The "c" it's a connection that I have done for have the possibility of charge the boiler.. (in this way the homeowner can use heating and warm water).. The red parts are tape...