Greenhouse heater problem
 

I have a problem with my paraffin heater it burns for around 5 hours then
stops. When i look at the wicks they have a hard carbon deposit on them.
When I knock this off I can relight them but they go out again in after the
same amout of time.I cant do this through the night ( I'm not that
dedicated).Also I've tried new wicks.

Be glad of your help

GaryB