Baxi Bermuda 401 ?

having just fitted a new electrical programmer after old one kept clicking and flashing and not lighting up central heating.I used the old base as I thought it would be the same as the new one.However I notice now that when I switch on central heating (as before)nothing happens,but if I switch that off,and switch on the hot water both the hot water system and the central heating heat up.The new programmer I fitted is a Honeywell ST699 single day timer. Does anyone know if the old base is suitable (or wiring sequence) as the printed circuit board on the old unit looks different to the new one Thank you