My oil boiler is heating water but not the house?

I have an oil heating system which heats the water and the house and was new last year. It worked last winter and we have since refille dthe oil and it continued to work. However, we have come to turn the heating on this week and it doesnt appear to be working, no heat is coming from radiators but the water is still hot! This seems very strange, especially as the Water is hot even its not meant to be. The immersion heater is not on. Does anyone know what might be wrong and what needs to be done to fix this.

Many thanks