A couple of times the past few months our combi boiler has either refused to serve hot water, or has cut out in the middle (fun in the shower !).
A quick restart of the boiler seemed to cure it, and it was logged as "must check that out" along with everything else.
Did it Saturday, so I dug out the manual, and started by checking the diagnostic codes, and then the fault codes. The last 10 were a mix of "unable to start" or "stopped" because of low gas pressure.
Initial reaction was (a) faulty boiler or (b) get the pressure checked.
Then, on a hunch, I checked the meter and discovered to my surprise that the cutoff valve (which takes a removable square-headed spanner) wasn't fully open ... the spanner was jammed against the wall, but removing it and rotating it gave at least another 1/3 of a turn.
So far boiler has been fine.
Maybe it really was low pressure - OK in the main but very sensitive to fluctuations (like the whole street turning their heating on in one go.)
AFAICR the last person to touch that valve was the fitter who installed a pipe run and termination for our gas oven - around 2011.