Well, spring is sprung and we've endured the beast from the east and I'd like to report that we stayed toasty right through the winter. This is the first winter in this house that we haven't had a central heating breakdown and I'm informed by the family that the house is warm all through with no cold spots........... Come back in the spring, and give us an update then.
The only thing I've had to do is a give a couple of tweaks to the lockshields of a rad or two that were screwed down to being just cracked open. They started to not get fully hot so I opened them all the way to 'blast them through' so to speak then put them back to practically where they were. Job done.
Thanks again for the advice guys. Much appreciated.