how to fix boiler with codes f1, f4 and f5 on a glow worm?

the boiler turns on when programmed then goes of with one of the following codes flashing under the red light, f1 f4 or f5. I turn the boiler off with the dial on the right and then back on, it fires back up but the problem returns. We have a glow worm 18sxi which is about 4 years old serviced every year. Any help would be very much appreciated