Help to identify drain plug on Grant Combi

[mylittlehouse]

Hello all
I added x800 to my heating system this morning as rads were cold at the bottom and ran it for a few hours.
Amazing stuff the rads all get nice and warm, next step is to drain the system and add x100.
I cleaned the magma clean which was caked in junk.
I Tried to open the drain value on the rad in the kitchen but its having none of it so i thought I would drain from the boiler I have a grant vortex pro combi.
There is two drain plugs one on the left and one on the right, i connected a hose to the one on the right and drained it down, water looked pretty clear but the pressure dropped to zero so I assumed it was the heating water.
I opened the towel rail upstairs and no water came out but the rads in the bedrooms all let water out when opening the bleed valves.
Any Anyone tell me where the drain value on this boiler is so i can drain out the x800 and refill or if I am missing something?
For reference I have put a photo below.
I used the drain valve on the red circle but there is another where the blue circle is.
Does anyone know this boiler?

 

[BoilerBob]

At the bottom on the left you’ll have to take out the burner first make sure the boiler is off. Bob

 

[mylittlehouse]

You just mean the red cover right, on the photo where the blue circle is i can see a drain plug but didn’t know if that was the hot water or the heating one.