Most boilers have a gauge on the front and has to have the needle set to at least 1.5/ 2.00 on the gauge otherwise it will swith it's self off to save burning the pipes out, underneath the boiler you should see a small copper pipe with a tap at each end turn them both inline with the copper pipe and watch the gauge till it reaches at least 1.5 then turn the taps off, the boiler should then work,
Hope this helps you and others.
Rick.
August 2016