my boulter buderus has fault code 2f and cant get hot water?

i cant get any hot water from my boulter buderus boiler, it has a fault code 2f which i have read up on and it means - The flow sensor and safety sensor have, after burner
startup, not detected any temperature increase in the
heating water, or they have determined that the
temperature difference between The flow sensor and
safety sensor is too high.

i dont know what this means and dont know what the sensors are! is there something i can do myself to fix i or do i need to get an engineer out?

kirsty
August 2011