A furnace that won’t turn on can be a huge inconvenience, especially when temperatures outside in Denver, CO, drop below freezing. There could be several things at fault, like a broken thermocouple or a dirty flame sensor. Both common issues can happen for several reasons. Keep reading to learn the primary causes and how to address them. These problems typically require professional service to resolve.
Malfunctioning Thermocouple
The thermocouple monitors a pilot light flame. Over time, it may malfunction, causing the flame to go out. When this happens, the furnace won’t be able to stay on, which means no heat for your house.
Age-Related Wear and Metal Fatigue
A thermocouple is under constant heat exposure, which can weaken the integrity of its metal and accuracy over time. The older it gets, the harder it becomes to generate a strong signal, which can interfere with the gas valve. The furnace may end up thinking the pilot light isn’t on when it really is. If this happens, the unit will shut itself off for safety reasons. Fixing a worn-out thermocouple often requires a full replacement of the component.
Improper Positioning Near Pilot Flame
The thermocouple always needs proper positioning to sense heat correctly. If it shifts even slightly, this can lead to ignition failure. This is why it’s so important to have a furnace professionally cleaned once a year. We’ll clean the internal components without bumping or bending the thermocouple. We’ll also be able to tell whether vibration has resulted in misalignment. If it has, we can reposition the thermocouple so it has proper flame contact.
Corrosion From Moisture or Contaminants
A thermocouple has an increased risk of corrosion when it has prolonged exposure to dust, moisture, and combustion byproducts. Buildup will interfere with its heat-sensing and signal-transmitting capabilities. Humid environments, such as basements, crawl spaces, or utility rooms, often accelerate the corrosion process. Parts close to the pilot assembly are also susceptible to airborne contaminants, such as lint or hair from pets. In some situations, it’s best to replace a corroded thermocouple rather than clean it.
Loose or Damaged Connections
Thermocouples have a small threaded fitting connected to them that attaches them to the gas valve. This connection must be tight and secure. If it becomes loose, the signal provided by the thermocouple may become inconsistent, causing the furnace to shut off unexpectedly. A damaged thermocouple line can cause the same problem. You should never attempt to repair this problem yourself. The thermocouple can crack if you don’t handle it properly. Instead, you should let one of our experienced technicians take care of the job.
Manufacturing Defect or Poor Build Quality
Your pilot light problem might stem from a thermocouple made of low-quality material. This is why you should always let one of our technicians perform the furnace installation. We always use high-quality components that prevent premature failure.
Defective Flame Sensor
If you have a newer furnace, it probably doesn’t have a thermocouple or pilot light. Instead, it will use a flame sensor. This sensor has the job of detecting the burner flame. When it fails, the furnace won’t stay on.
Carbon Buildup From Incomplete Combustion
Throughout the use of the furnace, a very thin film of carbon residue may form on the flame sensor. This often occurs when the combustion process isn’t completely free of impurities, which could be due to clogged burners or limited airflow. Even a small amount of accumulation can make the sensor and its flame detection capabilities inaccurate. For safety reasons, the furnace will turn off when it detects that the burner flame is not stable. We can usually fix this problem by cleaning the flame sensor and resolving any airflow or burner restrictions.
Exposure to High Humidity or Moisture
Moisture is just as big of an issue for flame sensors as it is for thermocouples. Furnaces installed in damp basements or utility closets tend to be more prone to corrosion. As time passes, the high humidity contributes to oxidation or surface residue that makes the flame sensor faulty. If you notice intermittent shutdowns during wet weather, this is a major red flag of moisture-related corrosion. We’ll have to inspect the flame sensor and its connections to see whether to clean or replace them.
Cracked Ceramic Insulation on Sensor
Your flame sensor may have ceramic insulation to protect the metal rod. If the ceramic cracks because of vibration, impact, or thermal stress, this will make the flame sensor unreliable. It may even short out electrically. We might be able to replace the ceramic-insulated flame sensor to fix the issue. If the damage is extensive, we may have to replace the entire flame sensor assembly.
Loose Wiring or Poor Grounding
The flame sensor needs a stable electrical path with proper grounding to accurately detect the flame signal. When the connected wiring becomes loose or corroded, the signal detection may drop out. Grounding issues can lead to inaccurate readings too, even if the sensor is clean. When this happens, the furnace may short cycle, preventing it from completing full heating cycles. We can often tighten loose connections to fix this issue, but some situations may necessitate wiring replacement.
Electrical Failure From Voltage Fluctuations
The furnace’s control board and flame-sensing circuit are both vulnerable to voltage spikes and unstable power. If the electronics mistakenly believe the flame sensor has damage, the furnace will repeatedly shut itself off. When this happens after a storm or power surge, it’s most likely the result of electrical damage. In some scenarios, the control board will fail while the sensor works fine. No matter the cause, a professional repair is crucial for restoring the furnace’s normal operation.
What Is the Process for Thermocouple or Flame Sensor Replacement?
Cleaning the thermocouple or flame sensor may resolve a lot of heating issues. But in some situations, the best move forward is to replace the faulty or damaged component. The replacement process is not a job suitable for DIY work.
When completing a thermocouple replacement, we start by making sure the pilot light problem doesn’t stem from a gas supply issue. Then, we shut the system off, remove the old thermocouple and replace it with a new one. We finish the repair by testing the pilot flame to ensure it stays lit.
For a flame sensor replacement, we start by inspecting all the connected wiring and the control board. This tells whether the sensor has failed or not. After we remove the old flame sensor and install the new one, we conduct multiple tests to make sure everything works correctly.
Get Expert Furnace Service Today
Summit Heating, A/C, Plumbing & Electrical gives you access to NATE-certified technicians for furnace services in Denver. We bring over two decades of expertise to each job. Whether you use a heater with a pilot light or flame sensor, we’ll make sure it runs reliably all winter. We even offer free estimates for heating systems that are ready for a full replacement. Our emergency furnace service works great for urgent heater problems that need immediate attention. Contact Summit Heating, A/C, Plumbing & Electrical today to book furnace service in Denver.
