Disclaimer: Due to the dangerous nature of working with electricity, we highly recommend hiring a qualified expert with the training and tools to help troubleshoot and install replacement parts safely. This information is not intended as a comprehensive guide. If you choose to perform any troubleshooting or replacement yourself, you do so at your own risk. Remember to ALWAYS disconnect the appliance from its power source before disconnecting any wires or attempting service tasks.
What is Resistance?
Resistance – Resistance measures how much opposition the flow of electric current encounters as it passes through an electric circuit. A high value of resistance means it is more difficult for electricity to pass through the circuit resulting in a low flow of current. A low value of resistance means the electricity can pass through the circuit easily, resulting in a high flow of current. Resistance is measured in units called Ohms and is often abbreviated with the Greek Omega symbol (Ω).
Resistance in stoves and fireplaces:
Testing for resistance quantifies how well the electric current flows through a part in your stove or fireplace. This is especially effective for testing igniters and switches. After verifying voltage is present and confirming the continuity of a complete circuit, the next step is to measure the strength of flow passing through the part.
Testing for Resistance
Warning: ALWAYS start by powering down, unplugging from the power source, and isolating the part you wish to test. Failure to power off and isolate the component being tested will lead to inaccurate and inconsistent measurements.
Tools you may need:
- The owner’s manual for the stove
- Wiring diagram
- A screwdriver set
- An ohmmeter or multimeter
How to measure resistance:
Not all meters will automatically detect the appropriate range of measurement; some meters need to be adjusted manually. If you do not know the expected range, start at the middle range setting, usually 20 kilo-ohms (20k), and adjust from there. Once you determine the correct range, use the lowest relevant range to ensure the most accurate measurement.
Begin by touching each of the multimeter probes to each end of the circuit or component you want to test.
If the value is zero – The range is too high and needs to be lowered
If the value reads “OL” (Overloaded) – The range may be set too low or the circuit may have no continuity.
Once the meter is set to a usable range, the resistance value will register a specific number.
Example #1: Igniters
Begin by powering down and unplugging the stove then remove the igniter. Set your multimeter to the lowest ohms setting to measure resistance. Touch the multimeter probes to each end of the igniter wires. A good igniter should register 30-60 ohms of resistance when cool. More resistance (less power flowing to the part) than this could prevent the igniter from fully heating up and could be too weak to light the pellets.
Example #2: Potentiometer such as the Dial-A-Fire on Enviro Pellet stoves
Some models of Enviro pellet stove rely on timer control modules as the “brain” of the stove. The start-up timer manages stove operation during the initial start-up cycle; then, the auger cycle timer works with the dial-a-fire switch to control pellet feed supporting continued stove operation. If adjusting the dial-a-fire has no control over the pellet stove, testing the potentiometer for resistance will help to narrow down which part should be replaced.
Note: To ensure accurate and consistent measurements, the dial-a-fire should be removed from the stove before testing. The dial-a-fire is found behind the right cabinet side of the stove.
- Begin by removing the dial-a fire located behind the right cabinet side of the stove.
- Set the multimeter to measure ohms (Ω).
- Touch the multimeter leads to the ends of the yellow dial-a-fire wires.
- The potentiometer should have a range of approximately 68KΩ to 850 KΩ (± 10%).
Full counter-clockwise (switched off) = open circuit, overload, or infinite resistance
Low fire - 800 KΩ to 900 KΩ
High fire - 68 KΩ to 82 KΩ (EF4 Timer Control 36.5 KΩ)
If the range is not close to this value, the dial-a-fire should be replaced. If the dial-a-fire demonstrates the right resistance, you should continue troubleshooting the timer module.
Example #3: Millivolt Gas Control Valve
Disclaimer: Due to the dangerous nature of gas units (sometimes explosive if serviced incorrectly), we highly recommend hiring a qualified expert with the experience and tools to help troubleshoot and install replacement parts safely. This information is not intended as a comprehensive guide. If you choose to perform any troubleshooting or replacement yourself, you do so at your own risk.
A standing pilot gas valve, referred to as millivolt, will have 3 electrical contacts, known as valve operating heads. These valve operating heads are labeled as follows:
- TH: thermostat such as a wall switch, thermostat, or remote
- TP: thermopile (The fat probe in the pilot assembly)
- TH/TP: connects to both the thermostat and the thermopile
If your fireplace randomly shuts down, or the main burner fails to light, measuring ohms of resistance helps to verify whether the control valve properly completes the circuit to support fireplace operation.
Note: Before conducting this test, disconnect all leads from the valve. Failure to disconnect all leads will result in inaccurate and inconsistent measurements.
Valve Operating Head Test
1) Set the multimeter to measure ohms (Ω).
2) Touch the multimeter leads to the terminals of the millivolt gas control valve.
Thermostat Circuit Test = TH/TP & TH
Thermopile Circuit Test = TH & TP
3) The appropriate resistance value will vary depending on the type of millivolt valve. Generally, a low, fixed value of resistance means the valve is good; however, infinite ohms or a reading of “OL” indicates the valve may need to be replaced.