My neighbour has had problems with his boiler electrics failing.A gas engineer said that this was caused by a very high mains voltage. Out of curiosity I checked mine with a meter and it is 256v. Is this very unusual and out of the ordinary.There is a substation two houses away from me.
supply has to be within 10% higher and 6% lower than 230v @ 50 hz You are well witjin that tolerance but from memory boilers have a protective device (can't for the life of me think of the name of it) which blows on overvoltage, think its more like 270 or 290v tho, Changed a few when the DNO drops a nuetral, Along with PSU's for most low voltage appliances
mmm 230+10% = 253, so 259 is hardly well within tolerance! Check it with a differet meter and see what you get, if it's still 259 give them a call