I replaced my own tank which developed a hole in the base after the sacrificial aluminum cathode crumbled to bits and fell down to the bottom of the tank and then proceeded to eat a hole in the copper through electrolytic action.
I bought a new tank for about £100.
Drained out the system using a hose pipe.
Removed the Honeywell Y system central heating which was in front of the tank buy closing the the isolation taps. Which prevented the central heating system needing to be drained.
Isolated the header tank with the inline gate valve.
Turned off the cold water supply.
Had to cut through any other pipes to the tank.
Thoughtfully, the previous installer had used a tank that needed pipes to be fitted to the rear of the tank. I suspect the airing cupboard was then built around the tank. I solved this problem by fitting short lengths of the hard to get to pipes to the rear of the tank before dropping the tank into the airing cupboard. These ended about 20 cm above the top of the tank allowing simple connection to the existing pipework using compression fittings.
It took about a day to complete and I had the help and advice of a friend who was also a plumber.
It's not any easy job, but is doable. Maybe get a few more quotes from other plumbers?
