I serviced a feroli optima (lpg)boiler today-first time it had been done for 7 years! DHW worked fine but CH would only get luke warm-gas pressure was minmum setting of aprox 7mb-checked thermistors-both gave the same reading and seemed ok,manual said increase gas pressure by turning up the p1 potentiometer on the pcb-i did this-had to turn it up to maximum to get the required 37mb max/7mb min and boiler now seems to be working fine,im was just wondering what is the cause of the problem??