Should a filling loop on a boiler be left off?

I have a combi boiler 30 HE and the water pressure has got too high, almost 4 and making a mooing sound. WE turned off the boiler last night and it continued to make noises. This morning the pressure is just over 2 with the boiler and gas still turned off. I think a dodgy plummer ( a few weeks ago) has been fiddling and has left the filling valve open.( So that he can come back and get more money off the landlord?)

There is water dripping outside from the overflow from the boiler. I traced this through the wall to the back of my boiler and there is a plastic valve ( switch/lever) on the right which was turned to the clockwide position. I turned it ( switched it the other way). Is this right. To the left of this plastic valve, underneath the boiler there are 3 other plastic valves. What are they for and what position should they be in?

Should I leave this filling loop valve in the anticlockwise position or put it back to the clockwise position?

The valve I am treating as the filling loop valve leads to a copper pipe that goes out oif the wall.

Do I need to do something to the other valves ( levers) underneath the boiler?

Any plummers with any advise?

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