if the orange fan running light is on when the boiler goes cold, get a corgi engineer to remove & thoroughly clean the fan blades/air pressure tubes as a common fault with this model is not enough air pressure in the boiler
either the expansion vessel on the back of the boiler is flat or the flexible tube going to it is blocked, or both. pressure relief valves tend not to reseal themselves when used.
the expansion vessel should be pumped to about 1/2 bar using a car tyre pump on the schraeder valve. when checking...
could also be a dead leg filling up with air on the hw circuit causing the boiler to stay on for hw momentarily, or if you have an intelligent washing machine sometimes the hot is not used & fills up with air
could also be a dead leg filling up with air on the hw circuit or if you have an intelligent washing machine sometimes the hot is not used & fills up with air
does sound very much like a sticking wax capsule. if i remember rightly located on the front of the storage cylinder/combimax. don't see them very often though