HI
turn water off to both taps.remove top caps (screws ? )
undo the nut holding the disc/cartridge .apply a bit of of grease on the threads (on the new cartridge).fit it to the tap.do not overtighten.refit taps.turn water on slowly.
HI
Remove old bath waste and cut the copper waste pipe straight so that you can fit straight compression coupler.
1.fit new bath combo waste
2.fit new bath plastic trap
3.use small waste pipe to connect the trap and old copper waste
HI
you need to bleed more.check other venting points including boiler vent,pump vent( front screw),
dont worry the air will be released evntually in few days and boiler will be normal.try to use the minimum heat setting on the boiler until the air clears.
HI
remove old trap and fit new anti vac trap (mcalpine)if this is not possible you can fit anti vac trap anywhere in the waste pipes (not main soil pipe).
HI
can you hear water bubbling from the flue when boiler is operational ?
this means that water flow is restricted from condensing pipe. otherwise
dont bother chasing pipe,elbows.problem is elsewhere.