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Steven Simmons

Technical Services Manager Southwest District

Flame Simulator

You go on a no heat call on a gas pack/ furnace. All the burners ignite, but then go out followed by the furnace showing an ignition failure code. After cleaning or replacing the flame rod, the furnace gives the same trouble. So, what now? What is the faulty component? The sensor, sensor wire, ignition board, or grounding?

There is a tool that can be used to verify the circuitry for the flame sensor. This tool can help you troubleshoot the components involved, which can prevent replacing parts that are not bad. We call this tool a “Flame Simulator”.
Safety First:
THIS TOOL SHOULD NEVER BE LEFT IN A UNIT BEYOND THE PARAMETERS OF TESTING. DOING SO WILL DIRECTLY VOID THE UNIT’S UL SAFETY LISTING.

What does it look like?

This tool is homemade and is a fraction of the cost of a store-bought simulator. There are a couple brands out there that can be purchased, but they are hard to find. It is customizable in the sense that you can add a small amount of wire to it or even an alligator clip to the bare end.

How is it made?

It is best to solder the connections to ensure they do not come loose.

How to use it

  1. Remove the female crimp connector from the flame rod within the unit.
  2. Connect the female connector to the male spade of the simulator.
  3. Call for heat on W1 with gas on or off.
  4. When the gas valve receives 24vac, touch the other end of the simulator to ground in the unit. If you have spark ignition, it will be sparking at this time. If you have Hot Surface Ignition then there will be a short period after it glows before the board is supposed to send 24vac to the gas valve.
  5. If you touch it to ground too early, the unit will give an “abnormal flame-proving signal” meaning: flame is proved while the gas valve is de-energized.
This will tell the board that the flame exists.

Results

If the unit repeats the ignition failure when using the Flame Simulator:
First: Verify that all of the ground wires are intact in the unit, primarily on the gas valve and the ignition board.
Second: Try the same test with a new wire from the board to the simulator.
Lastly: replace the control board.

If the unit does not give an ignition failure code while using the simulator but does when connected to the flame rod:
1st- clean the flame rod again
2nd- verify the DC Microamps while in series with the flame rod (Carrier is typically 4-6)
3rd-replace if out of range or in the bottom of the range (less than 5)

The items needed to make the Flame Simulator are best bought in multiples, so you should make your HVAC buddies one as well. Always remember, this is a tool and not a part.

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