the 330+ is made by Gloworm and is around £680 ish inc vat for the boiler itself.
its all very well saying the quote is expensive because its from BG, however notice the trace heater and the sealed system kit, perhaps the system is being sealed to avoid running new pipes through the house...........
My figure included those items but was based on the expectation of the boiler being £950 so fitting a GlowWorm would bring mine down to about £1600.
Having said that I would suggest my original price for a Viessmann with a five year warrantee.
Tony