sPoNiX wrote:
Doing mods to the central heating...

I notice my central heating has loads of gate valves (The ones with
the red handwheels) for isolating various parts of the circuit.

However, the 'fashion' these days seems to be to use service valves
(Ball valve with a screwdriver slot).

When I were a lad, gate valves were what we used before ball valves
became commonly available.

Gate valves were used in preference to globe valves
(stopcock/screwdown-tap types) on pumped circuits because they offered
little resistance to the flow. Their disadvantage was that they often
failed to fully isolate.

That's all now history, use full-bore ball valves.

Service valves have a reduced bore and are intended for use on water
supply systems where the increased resistance is of little concern. Use
full-bore ball valves on pumped heating systems.

Any other issues to be aware of?

The gate valves' glands are liable to start dripping if you do operate
them after a long time. The glands are probably packed with asbestos
fibre material. The 15mm gate valves must be worth at least 10p as
scrap.