yes you could do it yourself, but if you are not comfortable taking your boiler apart (a bit of a strip down required) I would get someone in to do it, you can get the part from your local supplier (heatmerchants etc) and the part number should be listed in your boiler manual, but in saying that, your plumber will get a healthy discount on parts over you so to get him out to do it will not cost a huge ammount over what it will cost you, and you will be sure it is right!
T, May 2008