Just fit em the cheapest, then youll get the job. Everyones a winner.
My parents Biasi has been in 12 years and still going strong
Granted its had a new pump, pressure relief, pcb x3, diverter valve, diaphragm, expansion vessel,fan x2, gas valve, pressure gauge x2, heat exchanger, shuttle assembly thingy and afew fuses - good boiler other than that though.
Mind you, its cost me afew quid so I'll probably be keeping it a little longer