My vokera boiler needs a an obsolete part?

I would get a second opinion before changing the boiler - if you can not get it replaced 'for free'.
What are the symptoms that made the gas man think the modulator was faulty?.

There are half a dozen common faults on these boilers - all readily fixed and none too expensive.
Hot/cold/hot/cold hot water tap - dirty venturi.
Boiler always on : broken dhw micro switch.
Boiler does not fire up - broken flow microswitch.
Boiler pilot goes out - broken flow microswitch.
Boiler does not turn on for hot tap/hot only when central heating on - holed dhw diaphragm (less often broken DHW microswitch)
Boiler does nothing (but hum from water pump) - stuck fan bearings.
Boiler pressure rises and vents when central heating warms up - Expansion vessel needs pumping up.

c#
February 2011

Honestly your best bet is to get it replaced, have you tried here http://www.britishinformation.com/boiler-replacement-grants/ to see if you qualify for a grant or go to your nearest citizens advice and see what they can do for you.

boiler bill
February 2011