Troubleshooting Quadra-Fire Thermocouples

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What is a thermocouple?

A thermocouple consists of 2 wires made from different kinds of metal that are joined at each end. When heat reaches the tip of the thermocouple in the burn pot, the energy splits and travels down the 2 wires creating a low voltage electric signal when the wires rejoin. This is measured in millivolts.

What does the thermocouple in a Quadra-Fire pellet stove do?

In a Quadra-Fire pellet stove, the thermocouple works as a low-limit sensor which detects the presence of a flame in the firepot. When a Quadra-Fire pellet stove is turned on, the control box runs through a start-up cycle for about 18 minutes. After completing the start-up cycle, your stove then relies on the thermocouple to sense the temperature in the firepot. The thermocouple signals the control box to call for more fuel when the fire reaches a specific temperature range. When the thermocouple senses the appropriate heat level in the firepot, it signals the control box to pause the pellet feed again.

To ensure the thermocouple accurately measures the heat level, the thermocouple and its ceramic cover MUST be positioned exactly right. The ceramic cover should extend 1 3/4 inches into the firepot and needs to touch the tip of the thermocouple wire. Incorrect placement of the thermocouple and/or cover could cause the stove to shut down unexpectedly.

Warning signs of a faulty thermocouple:
Over time, the wires of the thermocouple may deteriorate from exposure to heat. Common stove operation symptoms that indicate a thermocouple issue include:

-   Blinking yellow light on the control box  (some models may not have this feature)

-   Red call light on the junction box is on, but the fire in the firepot goes out

-   Stove stops feeding pellets after running for about 18 minutes

How to troubleshoot a Quadra-Fire thermocouple:

The simplest way to test a thermocouple is to check how much voltage it produces. To complete this test, you will need a digital meter that can measure millivolts (mV) of DC electricity and a lighter. Remember to unplug the stove from the wall before disconnecting any wires.

Note: If you feel like taking your test to the expert level, you can make an adapter wire with spade connectors. This adapter will allow you to measure voltage with the thermocouple still connected to the control box. This allows you to check that the red & green lights on the control box are turning on at the appropriate millivolt signal from the thermocouple.  The green light turns on at about 2.7 mV (+.5mV); the red light turns on at about 12.0 mV (+ 1mV).

  1. Set the meter to read about 30 mV of DC power and connect the probes of your meter to both ends of the thermocouple wire.
  2. Apply heat to the thermocouple tip in the firepot. The thermocouple should produce between 12-30 mV as it heats up.

The thermocouple should be replaced if it produces less than 12 mV.  If the correct voltage is present, check for a loose connection between the wiring harness and the thermocouple. The control box may need to be replaced.

Jan 15, 2021

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