Ducted gas central heater problem

[GreatP]

I have a 2 years old central heater that is not working properly. I really appreciate if somebody can help me to fix these problems.
The problems I have are:
1. The heat & fan running all the time even the room temperature is higher than setting temperature.
2. When switched on, the gas ignited. but as soon as fan started, the flame drop off. The cycle will continue with cool air blowing.
3. The first cycle workes OK, but following cycles without hot air.

 

[ollski]

Well I would guess at the fan stat, but without even knowing the make of the unit its just an educated guess.