Fireplaces, Heating Stoves, Flues and Chimneys - Gas Log Heater - Pilot Will not stay lit

I have model VL24PT manufactured by DESA international... I have had these logs for maybe 3 yrs and were cleaned last year... I am having trouble with pilot staying lit...There is a manual pilot start, but the unit has a thermometer on it that regulates temperature put out by the gas log heater...The pilot with stay lit throughout day and then at night will go out.... Sometimes it will stay lit throughout the night and sometimes not...What should i do...?

Also, if determined that a cleaning would simply do the trick, and in my case it would be....Then, I would appreciate instructions on making sure that i take the gas line of the log heater correctly.. Specifically, tools that prevent me from creating a spark and where to apply pressurized air without damaging the heating unit...I do not have an air compressor, but i have an attachment that would do the trick in the case of using an air compressor at the local convenient store...i would appreciate a quick response...

Thanks
Spencer