Well it only took about an hour and 3 people (Me, Glyn and Dave on Electrics, sound like a band eh :-) ). The hardest part was removing the old unit as the nuts securing the old pump had rusted on. After a little gentle persuasion we eventually succeeded in removing the old unit. Fitting and priming the new unit took about 10 minutes in total. We now have restored heating and Glyn won't freeze the next week and a bit while I'm off skiing. The irony ;-)
I've got a pub crawl to attend tomorrow so I had better make sure everything is packed when I get back from work. Luckily the flight is in the afternoon so everything should be fine. A good ending to the week!