Boiler Switching off Heatline compact s24

Hi all,
Well i think this is my first thread ,and you've guessed i have a problem so ill get straight into it.
Decided to install some Fernox F3 into my system as i have been cold spots on some radiators,ive used this before and its always done the trick.
Anyway i dropped all the water in the system from a downstairs drain off,but when it came to refilling the pressure gauge decided it wasn't going to play ball it was stuck on 2 bar.So right decided to remove the gauge to see if there was any crud blocking it up,anyway gave it a clean with a needle and refitted it,and that is all i have done.
The problem now is after i cleaned the gauge it's still not working correctly,so decided to refill anyway,but what i'm getting is the Boiler keeps cutting out after maybe two two or three minutes after the burners light.
???Does anyone have an idea as to what might be causing this,its bloody freezing in my house at the moment.

Air locked

SimonG said:

Air locked

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?Any pointers has to how i may put it right Simon,if it is an airlock.I have got a couple of radiators warmish up stairs,but downstairs are stone cold,but at least the Boiler is running for a tad longer before cutting out.Thanks for the reply.

Close all rads bar one until it gets hot then go from there.

SimonG said:

Close all rads bar one until it gets hot then go from there.

Click to expand...

Thank you i'll have a go at it tomorrow,gave up on it for now cheers.

If you have a external filling PRV like the one shown, ensure any isol valves on either side open (+ flexible hose connected up) open the black knob anticlockwise, if pressure still too low (assuming gauge now reading correctly) slowly turn the adjusting screw on top clockwise until you get 1.3/1.5 bar pressure, vent any air while maintaining this pressure, shut black knob when finished.