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Thanks bhg....I have a friend who is a plumber, and he is coming to have a look in the morning.
Now I recall, last night, just before the cylinder ran out, the gas flame on one burner, the one that runs when you want the least amount of heat, did flare up and sputter a bit. This sometimes happens when the cylinder is just about to run out. You can normally tell when a cylinder is about to run out as its starts to smell a bit.
So I shut it off, left it for a few mins, and then started it up again, which it did without any problems.