I have an elderly central heating system consisting of a Potterton Netaheat 16-22 boiler, with room and cylinder thermostats which give independent control of heating & hw by means of a 3 position motorised valve (Honeywell Sundial Y wiring). The Potterton room thermostat is now wildly inaccurate and i would like to replace it with a digital display. The Honeywell DT200 seemed a likely candidate, but I now understand that it has been replaced by the DT90E model which has TPI control. It sounds good, but will my old boiler cope with this new fangled technology?? If so, as it is a 2 wire model, do I just leave the neutral from my 3 wire system disconected?