If pilot flame extinguishes the moment you release the start button, thermocouple is dead. It tells the gas valve (magnetic valve) that pilot is lit. If no signal, valve closes gas for safety.
See if any of these signs match your device — each one increases the likelihood of this fault.
These are the causes we encounter while repairing Pilot flame keeps going out — ranked from most to least common.
Bad thermocouple (most common)
Clogged pilot jet
Low gas pressure
Burnt magnetic valve
Air in gas line (after long outage)
Clogged gas filter
Any of the following = a danger signal — call now and don't try to fix it yourself.
On-site diagnosis, clear pricing before any work, and a documented 6-month warranty.