Selgas
You got a mains pressure or a reduced pressure system there?
If it was reduced pressure I would be looking at the pressure reducing valve firstly.
If the clinder is feed from a “suppy tank” then it is likely you have a faulty ball cock valve and as a result you have now got an air lock in the system that needs bleeding out.
If it was mains pressure I would look at the inlet connection to the cylinder it may be all gummed up and restrciting the flow. 
Selgas Services Ltd
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