Usually, but it could be on a fused spur off the ring circuit.
If it has its own circuit, most likely 6 Amps if it's an MCB, or 5 Amps if a re-wireable.
Fused Outlet socket from a main socket ring. 3A fuse is plenty to supply boiler and valves, etc.
Separate outlet from consumer unit is unheard of .. ulless it is a special remote installation (like a boiler-house) or an external power arrangement and boiler system.