Problem with my Brittany boiler. Boiler on, no hot water - what is wrong?

have you tried topping the system up there will be a dial somewhere on the boiler either on the front or underneath if its in the red you will need to use the top up loop( two taps turn both on ) on the bottom of boiler where the pipes go in don't fill it up too much though only to 1 or 2 and no more there may bee a line as a guide fill to this line then turn the taps off again