OK, thanks for all that, warnings heeded. To clarify:
1. The work I did was overseen by a qualified CORGI engineer (my next-door neighbour) and every step was checked by him before being undertaken. I would never have attempted any work at all on the boiler had I not had his expertise to...
I am trying to replace the pressure switch in the above boiler. The original part has been superceded by a new design which has the tube connectors in an entirely different place to the old one. My problem is that I am not sure which tube connects to the positive terminal and which to the neg...