I have fitted a new 18hxi boiler,then wired it to my old wiring system it runs!!
but it won't turn off.
OK fit new Drayton room stat (RS1) new tank stat (HTS3) and new Programmer (Tempus 6) the only thing not changed is the mid position valve.
It runs!! But won't turn off.
the only way I get it to turn off is when it is not calling for heat and I turn the 230v supply off and back on, now it will stay off until the programmer next calls for heat.

any Ideas