Because I have a tricky plumbing problem to solve without replacing EVERYTHING in our heating system.
Anyone got a DH (or indeed yerself if you're really modern) working in central UK who knows about a wide bore steel one pipe system that we don't want to replace (just fit a new boiler to)? Think council and public sector plumbing circa 1950s and you/he will have the idea...
Will be very grateful and even consider paying travelling expenses for someone who really isn't an amateur 'rip it all out and put in a cheap combi' kind of guy...