motorised valve replacement

[littleh]

i need new valves and was wanting to replace them.
Ive looked up "normally closed" honeywell valves, can anyone advise what that means.
I know the ones i need are 22mm two way valves.
Is there a certain type i need or do all valves operate the same?
Thanks

[htg engineer]

Easiest way is to remove the actuator head and find the data badge that will tell you the make, model and serial number. Take this to a Plumbing / Heating supplies shop and ask if they have one.

Then all the wires are the same colour, so replacing shouldn't be too difficult.