Once this is complete go ahead and remove the pilot cover which will reveal two upright posts, one is the gas line for the pilot and the other is your thermocouple. When you push the thermocouple closer to the pilot, it will solve the problem. That has a copper wire that goes from the probe to your gas valve. In fact, the problems that affect gas furnaces typically involve the furnace's thermocouple, the pilot light, or some component of the electrical system. If the pilot remains lit, but the main furnace doesn’t stay lit, it may be time to replace the thermocouple. Our HVAC experts at PEACE OF MIND PLUMBING provide high quality furnace repairs that come with a 12 month no-hassle guarantee! A common culprit for this fault on Baxi boilers is a lack of pressure. home improvement and repair website. But whenever a boiler failure occurs, it’s never ideal and always inconvenient. Usually a furnace thermocouple is to blame when you can’t keep a pilot lit or if it is lit, the burners aren’t firing. There was a problem completing your request. Problems of Reference Junction Compensation : Thermocouples If the furnace’s pilot goes out, or the gas flow is interrupted then the thermocouple will automatically shut off the gas flow to the pilot, shutting down your furnace. NOTE: It is the temperature difference between the cold and hot junction that creates the millivolts. I'm having troubles with my furnace this morning. Your furnace’s thermocouple is a copper rod that sits next to your furnace burners.It’s often called the “flame sensor” because its job is to detect whether the pilot light is lit or not.If it can’t sense a flame from the pilot light, it prevents the gas valve from opening and … How to Replace Your Wall Furnace's Pilot... How to Replace Your Wall Furnace's Pilot Light. The thermocouple is the copper rod the pilot flame directly hits. Sometimes it's referred to as the "flame sensor." While some boiler problems are complex enough to warrant hiring Greenville heating and air experts, others can be resolved with a DIY approach. If you are unsure about what’s going on with your furnace or how to inspect or replace your thermocouple, make sure you contact a professional HVAC contractor to do the job safely! If there is soot build up on your thermocouple, then the issue might be resolved by cleaning your thermocouple. A thermocouple is the right hand man of the pilot light as it reads the pilots temperature on a rating, which tells it to keep the gas flowing. It sounds like your boiler is "surging". Before checking the gas furnace thermocouple you want to make sure that you have the gas shut off by putting the pilot setting switch to off and waiting a few minutes. Conclusion | How to Test a Thermocouple with a MultiMeter. Thermocouples fail, and must be replaced periodically. We welcome your comments and There was a problem completing your request. Asides from leaks, there are other problems that can cause a boiler to lock out including fault codes: 110 (overheating), to 160 (a faulty fan) or even 166 (air pressure switch fault). Turn on the furnace and light the pilot light following the manufacturer’s manual. The pilot light going out is one of the most common reasons that a gas furnace fails to produce heat. Then turn on the pilot again following the lighting instructions on your furnace and watch the pilot for failure to light. Thermocouple problems, drafts or clogs in the appliance may result in an unlit pilot light. If you are wondering, Intermittent thermocouple problems can occur if the pilot flame heats the lower 1/3 of the thermocouple. Several things can cause this, dirty boiler water or high pH level are the most common. You also want to make sure that you have the gas shut off, and the you set the gas valve to the off position. A gas furnace thermocouple is a small electrical device that acts as a safety device on a furnace. Check to see if you're getting 24 VAC at the terminals on the gas valve. A noisy boiler is often caused by “Kettling”, which is a build up of limescale in the heat exchanger. Water can become discoloured by minerals like iron and copper, which cause the pipes to rust. If the pilot in your boiler extinguishes on its own, your boiler probably has a faulty thermocouple. During your inspection of the gas furnace thermocouple, you will be turning the gas line on and off while making a number of slight adjustments and tests to determine if the source of your pilot problem. Tag : boiler thermocouple problems. Take the thermocouple to a hardware store for a replacement which is the same size on each end and same length or longer. If the pilot light is not operating properly, that could mean that soot has built up on the thermocouple. I had previously replaced the thermocouple without any problems. to this site, and use it for non-commercial use subject to our terms of use. Diagnosing a Thermocouple Problem If your pilot light ignites but won’t stay lit, then the problem is most likely related to your thermocouple , a metal sensor (about the size and shape of a sharpened pencil) that heats up by direct contact with the pilot light’s flame, telling your gas valve that the pilot light is lit so it’s safe to open the valve to let gas flow. I have replaced the thermocouple on my Rheem furnace after I could not keep the pilot lite with the old one, but the new thermocouple does not keep the pilot lite either even after 30 seconds of holding down the red pilot set button and then releasing it. If the pilot does not ignite, turn the gas switch off again, and wait the few minutes for gas dispersion. If you have removed the thermocouple nut from the gas valve and the pilot stays on, The gas valve is defective and must be replaced. Use a piece of steel wool to gently remove the soot. If this temperature is not being hit due to a weak flame from the pilot, the thermocouple will shut off the gas flow to the pilot and shutting down your furnace. There are some boiler problems, though, that may be resolved by the homeowner. Once this is done you can remove the pilot cover which will reveal two upright posts, one of which is the gas line for the pilot and the other is your thermocouple. View our Privacy Policy here. Please try your search again later. Be sure to use your pilot lighting instructions on the side of the furnace while going through the following steps to insure an accurate inspection. The tip of the thermocouple is positioned in the flame, keeping the tip heated at all times. You then need to let the furnace air out and cool down for a few minutes. Weil McLain Boilers – Common Issues 1. Sometimes the problem is simply that the thermocouple probe is too far from the flame. I've used this furnace for over 15 years without replacing the thermocouple. Unfortunately, replacing thermocouples inside a boiler or furnace requires shutting down the unit so it can cool enough for technicians to enter, remove the old thermocouple and weld a new one in place. Since the thermocouple data from this system can be input directly into Allen Bradley Control Logix PLCs via EthernetIP communication, mills have also used this system as remote IO to collect thermocouple data from other heat sources. But, sometimes, thermocouples wear out, then you may need replacing. The water in Calgary originates in the Rockies. The thermocouple needs to detect the flame, otherwise it will shut the gas valve, and your furnace will not function correctly. You can find a gas furnace thermocouple replacement at any good hardware store, or even on some on-line stores. The pilot flame must be big and hot enough to heat the thermocouple to the temperature it needs to generate enough voltage to signal the gas valve. You should get a reading of around 40 millivolts when the pilot flame is on. You must change a bad thermocouple as soon as possible. If there is soot build up on your thermocouple, then the issue might be resolved by cleaning your thermocouple. If your thermocouple is dirty, get some fine grain sandpaper and clean it off. The Boiler or furnace Thermocouple, what it does why it fails and how to replace it. I show how to bench test a thermocouple for a gas furnace using a multimeter. You must change a bad thermocouple as soon as possible. That is more of a catch-all time frame for thermocouples which may heat up (and thus generate current) more slowly. Thermocouples can last several years, but they don’t typically last as long as the furnace itself. Before you conduct this test, check the pilot flame. When a thermocouple fails, the pilot light won't stay lighted. You can use a pencil eraser to clean between the threads of the screw that attaches the thermocouple. Therefore, inspecting and testing your thermocouple should be part of your furnace maintenance. 1995-2018 MH Sub I, LLC dba Internet Brands. No Heat At All. Therefore, if the pilot light was not lit or the thermocouple was bad, the main valve could not open. All information is provided "AS IS." The tip of the thermocouple is called the hot junction and is where the two dissimilar metals join. The thermocouple is a probe that sits directly in the flame of the pilot light of your gas fired boiler or furnace or water heater or unit heater. A reading of less than 25 millivolts indicates that the thermocouple is bad and needs to be replaced. The thermocouple has nothing to do with the boiler short cycling on the low water cut off. Proceed cautiously with the diagnostic steps you take. The water in Calgary originates in the Rockies. Website operating On old furnaces, the standing pilot light can go out due to a strong draft, a dirty orifice in the pilot burner, or dirt in the gas tube. Common problems that may occur with it can sometimes be fixed by a layman with an idea of the mechanics behind it. Low boiler pressure is one of the most common boiler problems and it can have many possible causes. Make sure you have the correct replacement thermocouple. In almost all cases, the thermocouples are welded into place, which creates a horrendous problem when maintenance is needed. Signs of wear or corrosion of the wirings, e.g. Here’s a look at some boilers problems and ways to resolve them. Banging, gurgling, rumbling or whistling pipes can be caused by … Click to see full answer. HOME The thermocouple consists of up of a tube, a bracket, and wires. These are the top 10 most common boiler problems: Common Boiler Problems: Hot water but no heating; No heat or hot water; Boiler is leaking; Boiler is kettling; Noisy boiler (e.g. Like the other component parts in your furnace, the thermocouple can wear down over time, producing lower voltage than it should when heated. suggestions. It’s important to know how to keep a thermocouple clean and in working order. The tip of the thermocouple is positioned in the flame, keeping the tip heated at all times. Then turn on the pilot again following the lighting instructions on your furnace and watch the pilot for failure to light. What you will do is simply do several simple on and off tests to check your gas furnace thermocouple for issues. If the furnace still won’t work, the thermocouple is probably bad. If you cannot detect any obvious problems then it may be time to call an HVAC contractor to check the functionality of your thermocouple. 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