Fitting a Bleed Valve to Central Heating Pipes in Loft

[Sebast1antombs]

I live in a bungalow, the central heating pipes are in the loft, it's a sealed system, made of plastic pipe and pushfit couplers.
As the pipe work is in the loft bleeding the radiators doesn't get the air out of the system.
Should there be a bleed valve in the loft at the high point? as I cant find one.
Would fitting one be a good idea?
I've had to change one coupler that was leaking, the one next to it clearly has been, a 22mm even T with a 15 to 10mm reducer plugged onto a 22 to 15mm reducer and the 10mm pipe isn't fitted staight.
Replacing this with 22 /22/15 uneven T, a short run of 15mm with a T set vertically and a riser pipe clamped to a rafter capped with a drain cock , another short run of 15mm with a 15 to 10 reducer on the other horizontal leg to straighten the pipe run out is my plan.