The problem known as Fluctuating Flames occurs when gas pressure at the burner orifice changes in an erratic pattern, causing the flame to randomly lengthen and shorten, even with the burner controls left untouched. The service technician needs to check the burner orifice first for dust and dirt. If a blockage has been detected and removed, but the problem persists, then there could be a problem with the burner’s gas supply system. In industrial furnaces, the gas pressure regulator, or the gas pressure meter may be defective and will need replacement.

Unstable or Wavering Flames may just be caused by an external draft blowing across the burner which usually affects the pilot or igniting flame. Adding adequate protection or shielding will remedy the situation. However, if the burner’s main flame is unstable, this leads to incomplete combustion. There could also be a crack in the heat exchanger through which the draft passes. Such damages may be detected visually. Maintenance personnel will often look for soot and other types of discoloration to reveal these cracks. In this case, the heat exchanger needs to be repaired or replaced immediately.