Potterton PRT2/ EP2002 C/H always on (unless at temp)?

I have developed a fault on my Potterton EP2002 Programmer following short circuiting and blowing a fuse. The programmer is sending a constant live to the thermostat – meaning the Central Heating by passes the programmer and is solely controlled by the thermostat (thermostat is always on regardless of the CH begin on or off at the programmer)

The same programmer controls the Hot Water and which comes on and off as per the programmed time.

The Central heating works fine if controlled by the thermostat.

So the problem is either the programmer (Potterton EP2002) or the thermostat (Potterton PRT2) – can anyone advise which one is likely to be damaged if I blew the fuse by shorting the wires at the thermostat? (connecting neutral to linked live :s)

I have a new thermostat (Honeywell DT90e) which I could swap out if the thermostat is at fault – however as the new stat is a digital and only has room for 2 wires instead of the 3 in the PRT2 – I am reluctant to mess around with it further without some reassurance.