Strange timer fault on Halstead Best 50?

I have a Halstead Best 50 which works fine on HW timer but does not work on CH timer. If I switch to continous the CH works fine on the thermostat i.e. switching on and off ok with thermostat. Switch to timer and it does not switch on at all. I have tested the controller off the system with mains and it switches on/off ok with timer and noticed as far as outputs are concerned their is no difference between cont. and timer but my HW will not run.The system is pumped system with two motorised zone valves.
I am a bit stuck as the boiler and everything is ok when on cont. but will not time on CH but the HW works like a dream. Anyone any ideas where to look ( tested programmer/timer and thermostat both ok) ?