Worcester 19/24 cbi boiler?

hello i have a Worcester 19/24 cbi boiler it was working perfect till the other day but now it runs for about 3-5 mins then shuts down for about 3 mins then you can hear the fan and it firers up again,and so it carries on with the same cycle,it does not lock out .when it shuts down the orange light on the far left is on continuous then when it is running the far left light and the middle light stay on continuous,any help would be appreciated,thanks stuart