Quote Originally Posted by Edinburgh2000 View Post
It's an age thing, nothing to do with geography. In the 'old days' all the wiring for central heating systems was at mains voltage. Like DorrisMancer, my thermostats were all wired with three core + earth mains cable (6243Y 1.5mm2 cores; red, yellow, blue; later brown, grey, black). That cable is rated to 19 Amps (in conduit) - that's 4kW at mains voltage - far more than would ever be needed for a boiler and pump.
Okay. Never seen wiring like that myself, not even in the seventies home where my parents used to live, but I'll take your word for it. Either way be careful with electricity and when in doubt hire a professional to do it for you.