Three bar fire keeps going out

Question

I've got a three bar fire and it has worked fine up until lately. However, recently the flame on the front of the heater has been flickering and then the heater has been turning itself off. I bought a new gas cylinder thinking that it could have run out but the problem remains. I know that I don't have a leak in the pipe between the cylinder and heater, so I can't think what it could be. Thank you for your help.