Is your Baxi Duo Tec Boiler flashing E119 or E1 19? then it most likely means you have low water pressure

This video will show you what you need to do to increase the pressure on the boiler.

There are 2 black levers underneath the righthand side of the boiler. These levers both control the flow of cold water into the heating side of the boiler.

By operating these black lever valves it will top up the pressure on your Baxi and remove the E119 code. Your boiler should automatically start working again.