Thanks for your replies. On power on it shows 'lnp' in the top display and oC and pr in the bottom display. This would indicate it is set for PT100. It then changes to PV 100 and SV 0.0, then quickly changes to a flashing oooo in the top display and 100 in the bottom display. I have the probe connected through a din connector on the box rather than directly onto the pid. I think I need to dismantle the wiring and try it wired directy.