Heating not hot enough?

I have a Baxi Solo Boiler. The water appears to be hot but the heating comes on and automatically switches off before it reaches the temperature on the thermostat. Later it comes back on. This means that the house is never warm enough, but is either freezing or warm at best.

Please could you let me know what might be wrong?

Is there some sort of over ride or something? When it's not working properly the boiler says it's on but the pilot isn't on - The programmer is on for water and heating and the thermostat is on with the click around 15C and it's set to around 22C....

Please could anyone help?

Michael