Potteton boiler no central heating

[blaste47]

Having troubles with my potteton gold combi 28he a.
Water works completely fine however the central heating has seized to work.
When calling for heat, the boiler rad light comes on. The pilot light will ignite and stay on until 90 is reached on the boiler at which point it turns the pilot back on and it won't re ignite unless the temp drops down to around 20.
Have drained the system and tried draining the pump. Have also cleared the condenser bottle of any muck.
Thanks

 

[ShaunCorbs]

Did you drain the system before it started to do this fault ?

 

[blaste47]

Did you drain the system before it started to do this fault ?

I did not no, did it afterwards.
When it was working I probably bled the system maybe 3 weeks ago