Myson Orion fanfare 50 IS boiler?

The british gas engineer first fixed a control valve, then repaired a leaking isolator valve, then the boiler would only fire up with the mains switch clicked off then and the boiler would fire up. The timing clock was replaced, not altered the problem. Another engineer replaced the electronic circuit board and told us it may also be the TV suppressor a small white oblong 3 lead 2 black 1 earth lead, 1 black lead attaches to thermostate control on boiler and other black lead for pump and then earth. trouble is this part is no longer available? could this be the cause...boiler and pump both make a racket...air? and the boiler does fire up but then switches off? and may start or the old on/off power switch to the boiler.....I have looked at this and cannot figure out what is going on....any help much appreciated and can any one suggest if this part can be still purchased tried all usual outlets, if not, new boiler = ouch :)