Yep, fan runs constantly, just the speed ramps up and down.
Don't bother oiling the fan bearings, they fail quickly once they start to sqeak.
Google CET Ltd, they do recon fans for £60 ish, switch everything off, remove outer casing from boiler, disconnect fan conenctions, remove from its casing, remove replacement from its casing and put where old one came from, making sure its properly sealed, job done. Takes 10 mins max.
Nat, September 2009