My Vokera Linea 28 4 years old has just been serviced. I noticed the pressure was low and turned it up to 1 bar. Later after the heating came on it went up 2.5 bar. I contacted the engineer and he reckons that is normal. In the past I do not remember the pressure going up more than half a bar. Is it normal to go from 1 to 2.5 bar?