'Any idea what the cause of the prioblem might be ?'
By the way the cooker has a safety cover to cut out the gas if the flame should go out while the gas is turned on . However it stopped working approx a few months ago .
Could that have something to do with this current problem ?
I've no idea what the problem is, but when safety valve on my oven went a couple of years ago it was a flipping nightmare trying to find a man who can. No one seems qualified to touch gas these days except boiler engineers and they won't touch a cooker.