Never reaches correct temperature since install despite full on 240 deg setting. An internal oven thermometer shows this fact. Believ that installer may have installed incorrectly.Pilot ignition needs to be held on for about 5mins to light either grill or oven and then only with a low flame that is either on or off with hardly any movement in flame height. We are on normal mains gas - couls it have been installed on LPG? Could this be the problem?