I have a 10-15 year old Worcester Combi Junior 24i that kettles only on Central Heating cold start. This winter is the first time it's started doing it. When it kettles, if I turn off the boiler via the thermostat for a few minutes then turn it back on again it runs no problem until...
Just had the though the other day that, as hot water from combi boilers does not normally get exposed to any air and is always under pressure, is it technically safe to drink? :D
Not saying it would taste nice or be a recommended thing to do though!