E133 error code?

Hi

I have a combi boiler Promax Combi HE Plus A, i keep getting error code E133 which is a gas supply fault, due to the extremely cold weather lately and from what i could find out on google, i think it may be condensate drain system pipe that is frozen. As heating engineers cannot get to me immediatley (and for the sake of my 9 year old) I have scoured the internet to find out where this pipe is located (I,m not blonde) and apparently easiest way to thaw out is boiling water being poured over the pipe... thing is and excuse me if this seems really obvious to you all but
am I supposed to do that on the pipe inside or outside.. if it outside its going to be impossible as I live in a second floor flat.. please advise, thanks.. Kathy