The boiler is about 2 years old, water is heating up ok but when heating the radiators it will not reach desired temp and gets to about 20.5 to a max of 21.5 even if i set temp for 25.0. I have spoken to vaillant help line who talked me through reset, and there are no fault codes displayed. Any ideas?
There could be a number of issues with this scenario as you have stated it. How are you measuring the temperature at the radiators? In the past has the boiler managed to heat the room up to 25 degrees ok? It may be related the the selection of your boiler in the first place. You may have an issue with the controller, thermostat or temperature sensor. More information please.