After serious thinking wrote :

A Gaslow gauge will detect leaks on boats. Ensure all taps are closed then
turn off the cylinder valve. The gauge will show green. Check that the
gauge stays green for at least 24 hours.

Surely that would be a huge leak to empty the gas cylinder to that
extent in 24 hours.

You missed the bit about turning the cylinder valve to off. The Gaslow
will indicate the low pressure, if pressure is lost.

Basically the same idea as I suggested - turn all appliances off, turn
cylinder valve off, leave it a while and turn it back on - if there is
a hiss from the regulator, some pressure has been lost somewhere in the
pipe work.

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Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk