03 fault is not something you can repair yourself as you will have to go right into the boiler to fix it, call out a gas-safe registered engineer.
http://www.gassaferegister.co.uk/about/what_is_the_gas_safe_register.aspx?gclid=CLz0j-WYvLkCFbIPtAodlF0ApA
sinky7062, September 2013