We've recently changed from oil to gas and have a viessmann vitoden 100 , 26 kw condensing boiler installed. The house is well insulated and has 12 rads /3 zones . I've noticed that the with the thermostats set to 21 deg as before , the rads are lukewarm and dont heat up quickly . The room temp slowly ramps to the set temperature as I can see that the thermostat keeps cutting off frequently . Ive changed the boiler flow temp from the initial setting of 71 deg to 76 and then 78 , but that dosen't seem to have made a big difference. The only way to heat up to the same temp as before is to set the thermostat to around 25 , but even with that it seems that the boiler keeps cutting off and when its back on , its not On for long enough to heat up the rads .The boiler pressure is around mark of 1 bar . I've am obviously going to ask the installers to have a look again but any one has clues what could be the issue here ?