This is true for so many appliances and devices we have in our homes that need spare parts from time to time.
The contactor you mentioned is nothing more than a solenoid operated switch - a relay if you like. Many companies make and sell them - the Benedict & Jager contactor will very probably have dozens of competing companies making the same or similar switch - the artistry comes from being able to compare and select the most cost effective solution - most people will not be able to do that so they're at the mercy of the service agent.
A control board for a Boiler probably costs no more than £5 to manufacture - less if from China - but by the time the end-user gets it the cost is well over £100
Sadly there's no answer - flippantly your Stannah relative might move to a bungalow.
As for the overload switch you mentioned I can only assume it operates to disconnect power if too much current is drawn - like a circuit breaker perhaps.
It has been many years since I messed with electronics so my knowledge and any advice I might give is somewhat frozen in time.
If the maintenance contract does not include emergency repair and parts (call out AND parts) then it's a pretty useless maintenance plan.
All I can really offer is sympathy - sorry.
Use Google - select images - enter contactor and see hundreds of them - similarly overload switch.
Good luck...
Peccavi
June 2013
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