The pressure dropped and boiler went out. This happens occasionally and I usually turn the valve to refill. For some reason I didn't manage to turn it off quickly enough and the needle went really high. Usually I would just bleed a rad until the pressure dropped. Unfortunately have tried this and system keeps refilling. Suspect the valve I use to refill is not turning off properly but it seems tight enough.
Any ideas anyone? Have had heating on but of course it is spurting water out of the pressure release. Not sure how safe it is to have on but have no other heating.