There is a big red cylinder sited in the airing cupboard (not directly on top of the cylinder) and there is a pressure relief valve to the rear of the cylinder.
Hot water system sounded this morning like trying to boil kettle with no water. Turned everything off but pressure at zero and doesn't seem obvious that there is a water inlet valve to re-pressurise to 1 bar. Should there be? Is is that simple? If so how please?