In a gas fire, the radiant heat output from imitation coal pieces 2 caused to radiate by flames from a burner 1 is supplemented by convective air drawn into the base of the fire and passing through duct 6 before emerging through outlets 7, the duct being transversed by flue tubes 8, 9, 10, 11 to which combustion gases from the burner pass in the direction of the arrows B. A problem with such a fire is if the flue outlet 12 become blocked because the flow of gases reverses direction relative to the arrows B and the burner then combusts within unsafe limits if the doors 4, 5 are closed. To overcome this some of the flue tubes 8, 10 are provided with openings 10a, partially shielded by shield 22, to allow escape of recirculating combustion products into the convection duct, thereby allowing the burner to continue operation in safe limits in the event of flue blockage.