An aircraft company purchased a large used oven and had it moved to their location. They set up the oven and lit it, but it would not stay lit. The customer removed duct work and replaced the burner, but the oven still refused to stay lit.


Everything powered up fine for the ACES CSI called to the scene, but upon closer investigation he observed that the flame safeguard was lighting the pilot then dropping out. He determined there was no flame signal because the flame rod was not sensing the flame.

A flame rod is a metal rod that is installed so that it intersects and is in contact with the flame when the burner is lit. The rod is connected with a wire back to the flame relay and an electrical current is then passed through the rod. Because fire conducts electricity the flame relay is able to sense if the flame is lit or not. (This is a simplified explanation, for more information look up “flame rectification”.)


The CSI traced the wire to the flame rod. The flame rod had a rubber boot over the end of it and everything looked okay, but when he checked the rubber boot, it felt loose. He pulled it off and it was obvious the connector was broken.


The CSI installed a new connector on the end of the flame rod and re-lit the oven. The customer was happy that the ACES CSI was able to get them up and running so quickly.


Safety Concerns: Many times, while investigating a control systems scene, the CSI will observe safety concerns distinct from the initial mystery. In this case the CSI made note of several of these concerns:

  1. This was a large direct-fired oven, which meant the combustion products from the burner entered the oven work chamber. There was no make-up air for the burner so anyone entering the oven would be subject to large amounts of carbon monoxide.
  2. The exhaust was sent directly into the same room as the oven, potentially subjecting workers to carbon monoxide.
  3. There was no purge timer for the oven; if there was a gas leak and someone lit the oven, it could explode.

ACES proposed corrective actions for the make-up air and purge actions. The customer is awaiting repairs.