When i have run the hot water to the bath and turned the tap off the boiler will not reignite. This does not happen if we turn sink taps on or run shower.
Only difference, depending on how long it takes you to shower, is time on. So only possibility, is something sticking, after prolonged heating time. 3 way valve, with pressure switch etc etc. is the usual connection for HW or Heating, so look to that 1st, possible sticking on, so will not allow heating, or other after, not returning to normal position, service kits I believe are available.
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