CET Ltd : Suprima 80 boiler

[ChrisR]

"The electronics engineer makes his best judgement about the specification, etc. of PCBs"

That is a part of the argument, of course. An Engineer does not guess what a spec is. Unless it's supplied by the designer/manufacturer he doesn't have it, period. I was not saying that electronic engrs outside Potty can refurb Suprima boards!

 

[Agile]

The PCB designers for boiler circuits have several conflicting aspects to consider.

For example using plug in relays would have no advantage to the manufacturer and three disadvantages:-

1. Mechanical relay pin to socket connection a source of failure.
2. Extra cost of plug in base.
3. Cheap relay change possible by gas engineer does not sell replacement pcbs so loses considerable profit.

If you look at most boiler pcbs they use very cheap chinese relays at about 60p each. Many Ravenheat PCBs use "Finder" relays with heavy silver contacts at five times the cost but they last 100 times longer!

The fusible resistors on many Potty PCBs are intentionally used to protect the boiler if the gas valve, pump or fan fails low resistance. That is a good design doing whats intended !

Unfortunate that many less experienced engineers blow a second PCB because they fail to check the gas valve etc. first! Expensive mistake that which is perhaps worth doing just to learn about. ( And yes, I did it once when I started working on boilers !!! )

Another advantage to the manufacturer of fusible resistors is that if the gas valve fails then it blows the PCB and the supplier sells another one ( or even another two if its an inexperienced engineer! )

Tony Glazier