ow water temperature os my saunier duval SD623 boiler?

the heating works ok but the hot water is not very hot anymore. The boiler kicks in OK when the HW tap is opened and keeps running, but even with the stat set to max it won't give a hot bath. I'm guessing the the heat exchanger has become furred up. But looking at the price of the part alone £452 inc don't want to go that route yet.

mike french, September 2010