To top up a W-B combi when you can’t find a filling loop, chances are you need one of these.
Look up from under the boiler and you will see this. That is how the key is positioned to get it in.
A bit of silicone grease on the o-rings makes inserting them a lot easier. A tiny bit of hand cream will also help.
Now turn the key about 45 degrees clock-wise and it looks like this.
Just to make sure it does not fall out halfway through, tug it with twice the force it took to push in.
Now you can start filling by turning the white knob open, the same direction as you open a normal tap. 3 turns of 360 degrees is fully open.
When the pressure is correct, close the white knob GENTLY and pull the key out.
It is normal when a little bit of water spills out. If it keeps dripping, turn the white knob just a little further.
Remember that plastic is called plastic because it IS plastic. It will deform when closed with too much force and left that way at 60 degrees for a thousand hours.
NOTE: There are two slightly different Keys which WB’s use.