Honeywell Sundial y plan 3 position diverter valve ?

I am having problems with my Honeywell Sundial y plan 3 position diverter valve. I bought a replaceent synchron motor but although the original motor was faulty this did not cure the problem. I think the actual valve needs looking at. I have now manually pushed the leaver over on the valve in order to run both the HW and CH from the HW side of the electronic controler. I was only able to push the lever over and latch it with the motor unattached. Do I have to drain the system in order to take the valve off? Can you freeze the pipes? or could this be the micro switch on the valve?