Sorry for avoiding the question. The more important thing about the pump is the relative position of the cold feed/expension and the vent pipes. Preferably these should both be on the suction side of the pump, and close together. Numbering your visible pipes from left to right, top ones first, as seen in your second picture, and expecting the clean ones to be hot and the dirty ones to be cold. To give the correct answer I think we need to be sure what each pipe does:
1 is a cold 15mm pipe, probably the cold water main to a big tank in the loft
2 is a hot 22mm pipe, I see it comes from the hot water cylinder, so must be going off to feed the bath taps.
3 is a cool 22mm pipe, what does it do? Does it bring cold water from the big storage tank in the loft and deliver it to the bottom of the hot water cylinder?
4 is the air release when it goes upwards, and also goes into the boiler. When it goes downwards, is it bringing the water from the radiators (so will be cooler than pipe 5)?
5 (RHS of your picture) is a very hot pipe, comes out of the boiler and then goes upwards, is it the vent pipe that is bent over the small tank in your loft? Or, does it got into the bottom of the tank in the loft, to supply water to the system? The downwards run of this pipe goes to the pump, then a relief pipe with control valve. It continues down, can't see where it goes, can you have a look please? I would expect it to go to the 3-way valve but for some reason it does not go directly there.
In the lower picture the pipe going into the bottom of the boiler looks like the gas supply, so not relevant here.
Can you have a look round the pipes and see where they go please?
Also, have a look in the small feed and expansion tank, see what colour the water is, and what colour is any sediment on the sides and bottom of the tank.