Your boiler has been left in a manual testing mode after a service, which is preventing it from running at normal power.

DIY fix possible

Locate the two small control knobs on the front of the boiler used for temperature.Check the small white switch or dial often used by engineers during a service.Ensure both temperature dials are set to their normal operating positions and not turned fully to the 'minimum' or 'test' icons.Press the reset button for five seconds until the lights change.