I've recently had to replace a Honeywell dial style programmer with a digital ST6400C model. Whereas the old programmer had more ports and the live appeared to be 'looped' twice, the ST6400C replacement has less ports. I've wired it up according to instructions but the CH & HW can only operate independently, i.e. if the HW is on and the CH clicks in, then it overides the HW. Is there a wiring problem or a component problem with the system?
