It sounds like the burner and/or injectors are choked .Get the engineer back and have him fix it,ask to see his Corgi I.D.card and check to see whether he is qualified to work on fires.There should be a tick opposite fires on the reverse side of his card.
Gasman
August 2008
I can answer this question...
can the gas/air mixture be adjusted on a flavell firenza?
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix convector heaters.