en.wikipedia.org/wiki/Thermocouple

In appliance application, take a look at your water heater in the house. generally these types are electronic, in that they use a bi metal sandwich placed in the pilot flame. Since the heating of two dissimilar metals produces a charge, a small current is produced, and holds a tiny solenoid actuated valve open. This is usually in the range of 20mV.

Other types of thermocouple are available. Another type can use a liquid filled capillary tube and reservior. If the reservior is placed in the pilot flame the liquid in the tube expands and can exert force at the end of the capillary tube. This force can then be transmitted to hold the pilot valve open.

All this controls is the small amount of gas used to run the pilot flame, usually at a very low pressure (5" h2o) If the pilot flame goes out, then the element will not be heated, voltage or pressure are not produced, and the pilot feed valve closes, eliminating the possibility of unburned flammable gasses building up in some unconfined space waiting on some poor unsuspecting ignition source.

knagi we had a similar problem with the thumper beta version...a cheap fix would be to just adjust the position of the pilot...may work, may not...but the testing will include fireballs.