Boiler switching off

[cherroo]

Bled my radiators and didnt realize you shouldnt let any water out..duh i know...now boiler comes on for about 20 secs and switches off..please help..thanks

[buildersmate]

Presumably you have a direct pressurised system, so you have reduced the water pressure,.
It should run at a nominal 1 bar. Inside the boiler unit (underneath) will be a fill tube that you use to put more cold water from the mains into the system, and a gauge that should rise until one bar reading is reached.

[Catso]

Just for further help, our fill tube is in the airing cupboard, by our hot water tank.