Yes Tonny but how much per hr to change a rad. I bet I can find a good plumber for half your rate.
Then you'll be scratching your head as to why it doesn't heat up after the system is left riddled with trapped air cos' your plumber hasn't the time to bring it to temperature.
Get away you taking the **** now. or are you seriously suggesting a plumber cannot install a heating system.
An RGI is a Gas/boiler etc specialist with maybe limited plumbing skills.
Ok there are exceptions before to real plumbers turn up.