Combi boiler flame failure?

My boiler is currently struggling!! Sometimes it works and sometimes it doesn't.

The flame failure light often switches on and the boiler stops working. However, if you turn the switch to reingnite the boiler it will wokr for a couple of hours and then turn it self off again. This cycle continues....

Another thing is that the boiler makes a loud noise when starting up until it settles down and then occasionally in between.

The other thing to note is that we have recently taken the rads off and then back on again which has messed the pressure about recently.

Any help would be greatly appreciated.

Thanks in advance