Had a chap on the phone with an ecotec 824 the pressure on the gauge is going into the red when the boiler is first fired up on heating and the rads are scorching after about 20min all is fine,this only happens every few days apparently. My first thought's are expansion vessel pressure or packed up ,or blockage with crap in the expansion vessel hose ,there are no fault codes coming up just wondering if there are any common faults with these boilers as I don't do many repairs thanks in advance for any help .