Many moons ago I asked in here about the cost of work on my CH system, the consensus seemed to be the cost was not unreasonable.
The plumber spent three full days on it, finishing yesterday. He replaced the (uninsulated) copper cylinder with a green insulated one (stainless I think). In the process he moved th pump which was behind the old cylinder to under it (cylinder is on a shelf) and generally neatened up some criss cross piping, added some valves, removed some obsolete non-return valves etc. He then replaced the lounge radiator with a 6'6" x 20" double panelled rad (about twice the area of the old one) and replaced the other
9 rad valves with thermostatic valves.Finally re-filled the system and fired it up and went round and balanced the rads (we had quite a long discussion in here on that).
It was £2K including VAT (the pump re-positioning wasn't in the original quote). Only minor problem was a hum when the pump was running which I "fixed" by turning it down from 3 to 2.5 it it need replacing it will be a straightforward job now.
Really nice guy and an excellent "old fashioned" workman who spread dust sheets before him wherever he went!