Furnace Sequence of Operation


In this episode, Bryan talks to Justin Skinner about the standard gas furnace sequence of operation.

Regardless of the furnace type, it all begins with a heat call on W…

Then, the furnace checks the safeties to make sure ignition is possible and safe. If all systems are a go, the inducer motor comes on and clears a path for the exhaust. The furnace then proves that the path for the flue is clear, and a pressure switch closes upon sensing a pressure differential. The miracle of ignition comes next. There are a few different types of ignition, including hot-surface, intermittent spark, and standing pilot. Once the furnace opens the burner, it has to prove the flame.

Proving flame is somewhat similar to proving the flue path. A flame sensing rod creates a potential, and it determines if a flame is present by picking up microamps of current to ground. We're merely scratching the surface here, but the bottom line is that the furnace does a lot of checking and proving throughout the startup procedure.

Above all else, remember to check the fault code if the sequence of operation fails to complete. The absolute WORST thing you can do is restart the furnace, take the door off, or turn the furnace off. You lose a major troubleshooting clue.

Join Bryan and Justin as they talk about these furnace sequence topics:

  • Low Voltage Wiring
  • Boilers
  • Forced and Natural Draft
  • Flame rectification
  • Cleaning Flame Sensors
  • Gas Pool Heat
  • Silicon Nitride and Silicon Carbide
  • Hot Surface and Intermittent Pilot


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Richard C. Anderson
Richard C. Anderson
11/24/16 at 05:00 PM

The ASME Boiler & Pressure Vessel Code (BPVC) is an American Society of Mechanical Engineers (ASME) standard that regulates the design and construction of boilers and pressure vessels. The document is written and maintained by volunteers chosen for their technical expertise . And in addition to this some states have specific rules for boilers. Not all boilers in every state are only for hydronic heating. In Texas we have health and safety code 755 which regulates boilers. This can be for space heating, domestic water heating, process heating just to name a few.

    Richard Anderson
    Richard Anderson
    11/25/16 at 05:17 PM

    The comment was made that boilers are only for hydronic heating not for domestic water. That comment is not factual just wanted to share to ensure the facts were accurate sir.

      Bryan Orr
      Bryan Orr
      11/25/16 at 10:49 PM

      I think the sentiment is that the actual boiler water is not potable. A secondary coil can be used for domestic hot water. Is that incorrect?



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