So it's in Central Heating mode it seems. I.e. 'permanently powered'.
Turn the system off at the isolator. Turn your mains switch at your fusebox off if in doubt. The 3PV should now revert to Hot Water mode and you should feel firm spring pressure against the lever.
If not, then it isn't working. On most valves, you can take the actuator head off without draining and put the spindle into the half way between the two extremes position to allow both CH and HW at the same time, but you'll lose temperature control of the system. Still, if you want to run it under manual control, this might be the very thing.