Troubleshooting Quadrafire Pellet Stoves: Not Feeding Pellets
Snap Discs
Snap discs are used in a variety of ways and have many names, such as; Thermodiscs, Thermal switch, Bi-metal Switches, Fan Switches, Limit Switches, High Limit Switches, Low Limit Switches and Proof of Fire Switches. These switches have two or more wire terminals and inside the switch there is a disc that is coated with two dissimilar metals. Because all metals expand and contract at different temperatures, the surface tension of these metals together on a circular sheet of metal causes the disc to either have a convex or concave shape. Depending on which side of this disc is facing up toward the pin, the switch is either making a normally open or closed circuit at room temperature. When the switch detects heat, the metal on the disc will expand causing the disc to “flip” its convex or concave shape which allows the pin inside the switch to reverse its normally open or closed state. Bi-metal snap discs will automatically reset back to their normal state when enough of a temperature change is detected. Singular metal snap discs will have a button on the switch that must be manually pressed to reset the switch.
Most Quadrafire pellet stoves use 3 snap discs to control or monitor functions of the stove and are referenced as Snap Disc #1, #2 and #3 for most models. Models include the now obsolete 800, 1000, 1100i Insert, Mt Vernon OM (original model) and the Contour as well as current models still in production which are the Santa Fe, Santa Fe Insert, Castile, Castile Insert, CB1200 and CB1200i Insert.
The Mt Vernon AE. Mt Vernon E2, Edge 60 and the Trekker use a completely different set of controls but do have a drop tube power safety shutoff which is similar in function to Snap Disc #3. On these models, this is the ONLY snap disc that is used.
Troubleshooting Snap Disc #1
Snap Disc #1 (Convection Blower Power ON/ OFF) is usually located on the right side of the appliance. But it can be on the left side on some models. Models made after 2002 will all have 2 purple wires connected to it. This switch is going to power up the convection room air blower. This switch is always normally open, meaning that the blower circuit is not receiving power at room temperature.
Power is always present at snap disc #1 if the unit is plugged in regardless if the stove is running or not. This snap disc is not part of the feed motor circuit but if this switch fails to close, the stove or insert will overheat which would then trigger Snap Disc #2 to open the feed circuit and shut down the stove or insert.
- If the room blower is not coming on and the stove is overheating, unplug the stove, bypass snap disc #1 by connecting a jumper wire to the two purple wires and plug the stove back into the outlet. The blower should come on even if the stove is cold. If the blower does not come on, replace the blower.
- To test the switch, test for continuity across the terminals of the switch at room temperature. There should be no signal. If there is, replace the switch.
- If there is no signal at room temperature, heat the bottom surface of the switch with an open flame or heat gun, the switch should close after a few seconds for a closed circuit. If there is no closed circuit, replace the switch.
Notes:
- If snap disc #1 malfunctions the room blower is either on at start-up, which it shouldn’t be or the room blower never receives power and causes the stove to overheat. If the unit isn’t feeding at startup, snap disc #1 is not the problem.
- Snap disc #1 is located in different places on each model and will have different temperature values from one model to the next. Make sure you are ordering the correct snap disc #1 for your model.
Troubleshooting Snap Disc #2
Snap Disc #2 is always used to cut power to the feed circuit if an overheating situation occurs. Overheating usually happens when the convection room air blower fails to power up, either because the blower is bad or because snap disc #1 is open or fails to close.
An overheat event can also happen if the room air blower is excessively dirty or the blower is spinning slower than it should be for the user’s designated heat level output. For example: the blower is worn out and is not spinning at full speed even when full power is sent to the blower. Though it’s not common, overheating can occur if the stove, vent or vent cap is excessively dirty or restricted in some way.
Snap disc #2 is mounted in a variety of places depending upon your model and can be used in two different ways to achieve the same result.
If you have yellow wires at Snap Disc #2 It is being used indirectly to shut the feed system down as a “Thermostat Override Switch”.
Owner’s manuals refer to this switch as the “Thermostat Override” but not all models truly use the switch to override the thermostat circuit. If the wires on your snap disc #2 are any other color than yellow, skip to the next bold section below.
By interrupting the thermostat’s 18 volt circuit (opening the circuit), the demand for heat is interrupted and the fire will subside or go out. When this switch is used in this way, the switch will automatically reset when the unit cools back to a safe operating temperature, assuming that the thermostat is still calling for heat.
When snap disc #2 is used in this way and the unit is not feeding pellets at start-up, you must verify that the thermostat is calling for heat. When the TSTAT is calling for heat the circuit will be closed at both the thermostat AND the at snap disc #2. This is verified when the red call light on the junction box is illuminated. If the red call light is “ON”, snap disc #2 is closed.
- If the thermostat is calling for heat and the red call light is not illuminated; 1. If snap disc #2 is an automatic reset switch (no button to press for a manual reset), bypassing the switch with a jumper wire will close the circuit and the red call light should come on. If this happens, replace snap disc #2. If the light still doesn’t come on, the TSTAT connection may be faulty. Connect a wire across the TSAT terminals at the stove, if the light comes on, replace the thermostat, the thermostat wire or both.
- If snap disc #2 has a reset button, make sure the thermostat is calling for heat and reset the switch by pushing in on the button. You should hear a “click”. If the snap disc was in the open position the red call light should come “ON” and the stove should begin to startup.
If you have any other color wire connected to snap disc #2 other than yellow, this switch is going to be wired in series with other safety switches within the 120 volt feed system circuit. Testing all of these switches may be required for proper troubleshooting.
If the wires on your stove or insert are NOT yellow, snap disc #2 is being used to open the 120 volt circuit directly to the auger feed motor. Depending upon the model, the wires on your unit will either be orange and black, red and black, red and orange or just two black wires. When snap disc #2 is used in this way, the switch is going to be a manual reset switch. Using your Owner’s manual, locate snap disc #2 and press in on the button between the wires. You should hear a “click”. If your stove is “ON” and calling for heat, feeding should resume.
Troubleshooting Snap Disc #3 (Emergency Power Shutdown Switch)
Snap disc #3 is always located on the feed tube under the hopper in the back of the unit. This switch will always have gray wires attached to it if the unit was made after 2002. Some models will have gray wires that actually look sort of brownish. Snap disc #3 is ALWAYS a manual reset switch and is designed to kill power to the entire unit if a temperature of 250°F or more is detected in the feed tube leading back to the hopper.
This switch is normally closed to allow 120 volts to come in from the power outlet to the junction box control and wiring harness. When this switch is open it can be reset by pushing in on the button between the two gray/ brownish wires. If the switch fails to reset the stove will not receive any power and will need to be replaced. Likewise, if the switch is not staying closed and is opening up and random times, the switch should be replaced.
If this switch is triggered by an actual overheating event, a professional may need to be called in to repair the stove as there will likely be other damage taken to the feed motor or other parts of the stove.
Note: Manual reset snap discs, whether they are used as snap disc #2 or snap disc #3 are notorious for opening during power surge events simply by being plugged into the power outlet. The stove doesn’t even have to be “ON” for this to happen. If your stove isn’t working after some time of not using it this is most likely the problem.
