Hole in the wall gas fire

Sounds like Flame Supervision Device either needs adjusting or it is faulty. I does depend on the make of gas fire, but generally there is FSD on the fire that will check if the pilot light has light up correctly, if the FSD is not in the pilot light flame, it in effect assumes there is not flame therefore it shuts the gas valve safety device, to prevent the gas from running. To be honest it could be several things and I would recommend you get serviced or checked by A Gas Safe Engineer to be sure.

The most common fault would be a failed Thermocouple but there may a number of other possible faults. A problem with an appliance like would require a Gas safe registered engineer qualified to work on gas fires to safely resolve the issue.

Could be a few things, a gas safe engineer would be required to investigate.

Flame Supervision Device (FSD) or flame failure device (FFD) is used on gas fires to make sure that correct flame ignition has been completed. Usual problems with live flame fires is soot collecting around pilot from carbon forming on coals/logs etc. Simple service procedure usually enough to repair