| Part 2 Mismatching The Furnace & Thermostat |
| Common Thermostat Problems ...more advanced to follow, but start with the basics first. Work with the power off whenever possible. When a furnace does not work it may be caused by problems with the furnace or the thermostat. Before troubleshooting your thermostat, check to see if all filters are clean and all hoses to and from the units themselves are free of wear. If these are not causing problems, then it is time to look at specific thermostat issues and possible solutions. Your thermostat could have aging wiring that is faulty or the transformer may require replacing. A thermostat may need cleaning to eliminate erratic operation. Accumulated dust is a common culprit. First, you should have a small paintbrush, a screwdriver, and a voltmeter. The anticipator is a small metal tab positioned in front of an arcing printed scale. Give it a light push in both directions. This easy step may solve the problem. Give the thermostat's interior a light dusting with a small, soft paintbrush. Be sure to clean the contacts, which are small metal plates within the unit. The wires coming from the transformer attach to the contacts. Do not touch any of the interior parts with your fingers. For a wireless system, make sure you are using the correct batteries: AA Lithium. If the system is running at inconsistent times, then you may have inadvertently installed alkaline batteries. Regular batteries will run out of juice quickly in a wireless system, especially if the backlight is on or used frequently to check the readings. Does the heater or air conditioning fail to come on when the home's temperature is too cold or too warm? Or does it trigger on when there is no need? Is the thermostat installed in the proper location. This is very important as a thermostat installed on a wall that has high heat gain or heat loss will never offer you comfort as it will react mostly to the temperature of the wall and not the air in the living space. Additionally, thermostats installed where direct sunlight can hit the thermostat is going to be a problem also. A thermostat located near an outside door or window will be affected every time the door or window is opened or closed. A thermostat should be located close to the return (where the filter is installed) so that it senses and reacts to the air returning to the air handler for conditioning. Additionally, thermostats located near heat sources like hot or cold water pipes, radiant heaters, fireplaces, electrical devices which produce heat, etc... will never offer accurate temperatures and conditioning for the space. Is there a big hole behind the thermostat that will feed cool or warm drafts to the back of the thermostat? All thermostats have a hole behind them where the wires come into the thermostat from the air handling unit. Check this and if you find a big hole behind the thermostat stuff some insulation in this hole and cover it with a piece of tape. This will prevent drafts from affecting the thermostat. Has the heating anticipator been properly set by a qualified air conditioning and heating technician? The heat anticipator is on mechanical non-digital thermostats and needs to be set according to the amp draw on the heating control circuit. The heat anticipator offers a small amount of energy savings and prevents thermostat overshooting for you as it shuts off the main burners because the fan will continue to run and dissipate the heat which remains in the furnace or heat. Digital and programmable thermostats have built in heating and cooling anticipators which automatically set themselves without any manual adjustments. The mechanical thermostat needs a manual adjustment and you need a tool called an amp meter to determine the proper setting or see the tutorial on DIY heat anticipator adjustment. The cooling anticipator in the mechanical thermostat requires no manual adjustment. If you have a mechanical thermostat with a mercury bulb switching mechanism inside it, then this type of thermostat needs to be level. If the thermostat is not level, you'll never get an accurate temperature in the residence or business. Also check the power switch, which should be located near the air handling unit. It is not uncommon for people to mistake these switches for a light switch and turn them off. They unknowingly just turned the power off for their air conditioning and heating equipment, including their thermostat. Is your programmable thermostat is always losing its program? This is most likely one of the older thermostats that use the power from the air conditioning and heating equipment and every time you lose power you lose the program inside the thermostat. Programming an air conditioning and heating programmable thermostat can be a chore for many people to figure out so a problem like this can be frustrating, especially if you live in an area where there are constant power failures. The only solution to this problem is to replace the programmable thermostat with one that uses power stealing technology (it uses power from your air conditioning and heating system to hold the programs) and has a battery back-up, just in case you lose power. This can save you lots of trouble and frustration in the long run keeping you from reprogramming the thermostat over and over again when power failures occur. The back display light for the digital thermostat does not function, but the air conditioning and heating system works fine. Check the batteries, as some digital thermostats require AA or AAA batteries for the back light to function on the thermostat. There are two main types of digital thermostats; digital thermostats that use batteries for the back light to function and digital thermostats that use the power from the air conditioning and heating equipment. If you don’t know which kind of air conditioning and heating thermostat you have then open the thermostat up and look inside. If you don’t see any batteries or a battery compartment inside the thermostat then your thermostat uses power stealing technology. It is probably an older model digital thermostat and if it is a programmable thermostat, then every time you lose power you will lose the program inside which takes us to the next step in air conditioning and heating thermostat troubleshooting. Check the power switch and breaker to ensure the power is on before assuming you have a broken thermostat. If the base is loose, re tighten the screws. Check the wires coming from the transformer. If any corrosion is present, remove the wire from the contact and clean. Use a wire stripper to remove the surrounding insulation, cut back the wire, and reconnect. Make sure the terminal screws are tight. Try this quick test to detect a faulty thermostat... A thermostat's terminals are marked with "Y," which is usually a blue wire, "W" is a white wire, "G" is typically black, and "R" is red. You can use a short piece of wiring with the ends stripped away to create a "jump" between connections. The electricity will need to be on for this test. Place one end of the jump wire on the Y and the other end on the G - if the fan comes on during this connection, your thermostat could be faulty. You may need to test the transformer if nothing seems wrong with the thermostat. You can use a voltmeter or a multi tester. If you are using a multi tester, set the dial to ACV 50 and connect a probe to each of the terminals. This step will allow you to test for current. If there is none, one final step should be to check power coming in to the transformer. Use the multi tester or voltmeter to probe the hot wires and the neutral wires and tighten the contacts if necessary. If the problem is with an older thermostat, and the system is not on a heat pump, you should consider replacing the thermostat with a digital model. It will increase the efficiency of your unit and many styles are available that can be programmed to suit your daily schedule. Even if your system seems to be having problems not listed here, try the troubleshooting tips first. You may be able to solve the problem and avoid the expense of calling an outside professional. See How to Troubleshoot a Gas Furnace for information on possible furnace problems, causes and repairs. Faulty Thermostat Troubleshooting Problems & Repairs If the temperature of your house is going haywire, this may be a sign of a faulty thermostat or aging equipment. If your system is very old, you may want to consider replacement. These repair suggestions will work for the most common name brand, low voltage thermostats on the market today. This type of thermostat runs off of a transformer reducing the incoming line voltage from 120 volts down to between 12 and 24 volts, depending on your furnace. Your House Has No Heat Things To check for:
For a wireless system, make sure you are using the correct batteries: AA Lithium. If the system is running at inconsistent times, then you may have inadvertently installed alkaline batteries. Regular batteries will run out of juice quickly in a wireless system, especially if the backlight is on or used frequently to check the readings. Repair Checklist: • Reset circuit breaker or replace fuse. VIDEO: How to change a fuse •Give the thermostat's interior a light dusting with a small, soft paintbrush. Be sure to clean the contacts, which are small metal plates within the unit. The wires coming from the transformer attach to the contacts. Do not touch any of the interior parts with fingers. •The anticipator is a small metal tab positioned in front of an arcing printed scale. Give it a light push in both directions. This easy step may solve the problem. • Set the thermostat to its lowest setting and clean the bimetallic coil with a soft brush or compressed air. Set the thermostat to its highest setting and clean the coil again. Reset the thermostat to its desired setting. • If the base is loose, retighten the screws. Check the wires coming from the transformer. If any corrosion is present, remove the wire from the contact and clean. Use a wire stripper to remove the surrounding insulation, cut back the wire, and reconnect. • Check for loose connections or disconnected wires on low-voltage transformers usually mounted on the furnace. • On electronic models, check to see if the display is working, indicating power. If it is not working, replace the batteries in the electronic thermostat. Heat Either Does Not Reach or Exceeds the Set Temperature Things To Check For: •Thermostat is not level on the wall • Heat anticipator needs adjustment Possible Repairs • Level thermostat . • Heat Anticipator Adjustment. Furnace Turns On and Off Frequently ("short cycling") Things To Check For: • Thermostat components are dirty - accumulated dust is a common culprit • Heat anticipator not set correctly. Possible Repairs • Give the thermostat's interior a light dusting with a small, soft paintbrush. Be sure to clean the contacts, which are small metal plates within the unit. The wires coming from the transformer attach to the contacts. Do not touch any of the interior parts with fingers. • Heat Anticipator Adjustment |
| Troubleshooting A Home Furnace Thermostat |
Topics Covered:
* Common thermostat problems
* How to test if a thermostat is defective
* Troubleshooting problems & repairs
* Mismatching the furnace with the wrong
type of thermostat
* MILLIVOLTAGE
* LOW VOLTAGE-how to fix
* LINE VOLTAGE-how to fix
* What to look for when identifying your furnace
& thermostat type
* Troubleshoot a gas furnace
VIDEO: Replacing a thermostat
* Common thermostat problems
* How to test if a thermostat is defective
* Troubleshooting problems & repairs
* Mismatching the furnace with the wrong
type of thermostat
* MILLIVOLTAGE
* LOW VOLTAGE-how to fix
* LINE VOLTAGE-how to fix
* What to look for when identifying your furnace
& thermostat type
* Troubleshoot a gas furnace
VIDEO: Replacing a thermostat
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Introduction It is very important that your furnace and thermostat are compatible together. If they are not a suitable match, this will create operational and safety hazards. Please do not overlook this. There are multiple types of thermostats on the market and they are designed very differently. • Millivoltage • Low Voltage • Line Voltage Keep reading to find out which Thermostat System you should be using with your particular furnace. Millivoltage System Millivoltage is very rarely used in a residence. A Millivoltage System could be found in homes using direct/top vent wall furnace. Examples of their use may include: *** Gas Logs or Fireplaces Gas logs and some older forced air gas furnaces can work on a millivolt thermostat. To determine if a milivolt thermostat is need when making your thermostat selection refer to the owner’s manual or consult an HVAC professional. *** Some Forced Air Furnaces (Older Models) Technical Note: It is important when selecting the proper thermostat to know if your system has a single transformer or a double transformer. Some split systems will have a transformer for the heating and a transformer for the air conditioning system. This will make a big difference in the type of thermostat you select. If the system has two transformers then the thermostat selected must have an RC and RH terminal to separate the circuits. Low Voltage System A Low Voltage system is the most commonly used system found in homes. LOW voltage thermostats are typically used to control central heating and cooling systems. A LOW voltage thermostat should only be used with Cadet heaters if the amperage load exceeds the rating of the line voltage thermostat and only when combined with a relay. Low voltage programmable thermostats incorporate a step-down transformer to decrease the operating voltage from 120-volts to 6-volts, 24-volts or 30-volts, with 24-volts being the most common. This type of thermostat is used on most gas furnace systems in the United States and will have a series of very thin, multi-colored wires attached to it. They are the most versatile. The transformer is usually mounted on or near the furnace. These thermostats may be digital, electronic programmable, mercury bimetallic or mechanical contact type thermostats. Examples of their use may include: Air Conditioning Only Split System 99.9% of available low voltage thermostats will accommodate the Air Conditioning Only – Split System control. Gas Furnace 99.9% of available low voltage thermostats will accommodate the Gas Furnace Only control. Oil Furnace Only 99.9% of available low voltage thermostats will accommodate the Oil Furnace Only control. Electric Furnace Only 99.9% of available low voltage thermostats will accommodate the Electric Furnace Only control. Boilers (Steam or Hot Water) 99.9% of available low voltage thermostats will accommodate the Boilers (Steam or Hot Water) control. Heat Pump Only Be careful when selecting a thermostat for a heat pump. Not all thermostats support heat pumps so make sure you read the box of the thermostat to ensure you get a heat pump thermostat. Heat Pump w/Auxiliary Heating (Electric, Gas, or Oil) Be careful when selecting a thermostat for a heat pump. Not all thermostats support heat pumps so make sure you read the box of the thermostat to ensure you get a heat pump thermostat. It is important when selecting the proper thermostat to know if your system has a single transformer or a double transformer. Some split systems will have a transformer for the heating and a transformer for the air conditioning system. This will make a big difference in the type of thermostat you select. If the system has two transformers then the thermostat selected must have an RC and RH terminal to separate the circuits. AC with Gas Furnace Ensure the thermostat selected has air conditioning and gas furnace options available. It is important when selecting the proper thermostat to know if your system has a single transformer or a double transformer. Some split systems will have a transformer for the heating and a transformer for the air conditioning system. This will make a big difference in the type of thermostat you select. If the system has two transformers then the thermostat selected must have an RC and RH terminal to separate the circuits. AC with Oil Furnace Ensure the thermostat selected has air conditioning and oil furnace options available. It is important when selecting the proper thermostat to know if your system has a single transformer or a double transformer. Some split systems will have a transformer for the heating and a transformer for the air conditioning system. This will make a big difference in the type of thermostat you select. If the system has two transformers then the thermostat selected must have an RC and RH terminal to separate the circuits. AC with Electric Furnace Ensure the thermostat selected has air conditioning and electric furnace options available. It is important when selecting the proper thermostat to know if your system has a single transformer or a double transformer. Some split systems will have a transformer for the heating and a transformer for the air conditioning system. This will make a big difference in the type of thermostat you select. If the system has two transformers then the thermostat selected must have an RC and RH terminal to separate the circuits. AC with Boiler (Steam or Hot Water) Ensure the thermostat selected has air conditioning and boiler options available. Some thermostats may say heating only while others may be more specific and mention steam or hot water boiler systems. It is important when selecting the proper thermostat to know if your system has a single transformer or a double transformer. Some split systems will have a transformer for the heating and a transformer for the air conditioning system. This will make a big difference in the type of thermostat you select. If the system has two transformers then the thermostat selected must have an RC and RH terminal to separate the circuits. All Package Unit Combinations See various thermostat/equipment combination options for split system/stand-alone heating and air conditioning systems. Multi-Stage Air Conditioning This thermostat should have Y1 and Y2 terminals for multi-staging of cooling. This means you have an air conditioning system with two compressors or a single compressor that is capable of running at two different speeds or capacities. There is a temperature differential that will engage the second stage of this thermostat to start the second stage of cooling if needed. Usually a 3 degree differential setting is typical for the second stage to kick in and provide additional cooling. Some thermostats offer you the ability to change this differential to suit your comfort level. Multi-Stage Heating This is the same as the multi-staging thermostat for air conditioners except this thermostat should have W1 and W2 terminal instead of Y1 and Y2 terminals. As with the Multi-staging air conditioning thermostat the multi-staging heating thermostat will also have a differential of approximately 3 degrees before the second stage calls for heating. Some thermostats offer you the ability to change this differential to suit your comfort level. Multi-Stage Heating and Air Conditioning This thermostat will offer Y1, Y2, W1, and W2 terminals for multi-staging heating and air conditioning systems capable of multi-staging. See Multi-staging heating and air conditioning above for further details on staging and temperature differentials with the thermostat. How To Fix A Low Voltage Thermostat While low-voltage thermostats are very reliable and rarely defective, thermostat-related problems, such as faulty wires or loose connections, may cause a failure in your heating or cooling system. The problems are easy to identify, and just as easy to fix by making the appropriate repair or by replacing a faulty thermostat. DIFFICULTY: Moderately challenging Things You'll Need: Soft artist's paintbrush Neon tester Batteries Batteries Batteries Replacement thermostat Tape and pen Level or plumb line Screwdriver Wire cutters/strippers STEP 1 Turn off the power to heating and/or cooling systems at the main service panel or system shutoff switch. STEP 2 Remove the thermostat. On some models, remove the cover plate and then unscrew the thermostat body from a wired base plate secured to the wall. Other models plug into the base plate without screws. STEP 3 Remove any dust from the thermostat and base plate with a soft artist's brush. STEP 4 Check for broken, frayed or corroded wires and loose wire connections. Tighten any loose connections. Use wire cutters/strippers to cut damaged wires and strip off about 1/2 inch (12 mm) of insulation, then reconnect the wires. STEP 5 Restore the power to test the thermostat. Consult the manual for your thermostat and disconnect the power wire (usually red), then touch it to the terminal for the heat (the terminal marked as W with white wire from heater's transformer). STEP 6 Similarly, bypass the thermostat to check its cooling function by touching the disconnected power wire (red) to the terminal for the cooling system (typically yellow or green). STEP 7 If one or both systems fail to start, turn off their power, then identify (see step 8) and replace any faulty wires between the thermostat and the low- voltage transformer(s) at the heating or air-conditioning units. STEP 8 One way to test thermostat wires--on your heating system, for example--is to disconnect the wires from the thermostat and transformer, wire them together at one end, and test for continuity at the other end by clipping a continuity tester to one wire and probing the other wire. If the tester fails to light, replace the wires. STEP 9 Check for loose low-voltage wire connections at the transformer or loose line-voltage connections to the transformer. STEP 10 If both systems activate, replace the faulty thermostat Tips & Warnings If you don't have the installation instructions for your thermostat, go online to the manufacturer's web site and download them, or call to have them faxed or mailed. Make sure disconnected thermostat wires don't slip inside the wall. Pull them out a bit and either tape them to the wall, bend them or loop them around a pencil. If you're replacing a thermostat, choose a programmable model that allows nighttime setback for heating or daytime setback for cooling. This could save up to a third of your energy bill. Unless power is required for low-voltage testing, always shut the power off and follow the manufacturer's wiring instructions. Accidental wire contact or improper connections may damage the thermostat. While low-voltage wiring cannot hurt you, it can startle you, and that may cause an injury. Work with the power off whenever possible. Line Voltage System A LINE voltage thermostat should primarily be used for zonal electric heat systems such as: Electric fan forced heaters Electric baseboard Heaters Line voltage thermostats are powered by a 120-volt or 240-volt circuit, depending on the heater. This type of thermostat has thicker wires, like those used throughout your home. How To Fix A Line Voltage Thermostat DIFFICULTY: Moderately challenging Things You'll Need: Neon or continuity tester Masking tape and pen Replacement thermostat Screwdriver STEP 1 Turn off the power to the heater at your main circuit panel. Remove the thermostat cover plate. Remove the mounting screws and carefully pull the thermostat away from the wall or heater, and the wires out of the box (see illustration). STEP 2 Remove one wire nut at a time to test for power with a neon or continuity tester. Probe the grounding wire with one lead and each uncovered set of wires with the other lead. Proceed if the test light does not glow in any test. STEP 3 Identify the house wires that connect to the wires identified on the thermostat as line. Typically they're red. Mark some masking tape with the word line and put it on these house wires. Disconnect all wires to remove the thermostat. STEP 4 Place the thermostat on a table and tape down the wires so you'll have a hand free to rotate the tester knob. Use a continuity tester to test the thermostat. Clip a lead onto a black wire; probe the red wire on the same side of the thermostat while rotating the dial through all the "On" positions. The tester should remain lighted. Repeat for the other set of red and black wires. STEP 5 Replace the thermostat if it's defective. Reinstall a working one and call a professional to service the heating element Tips & Warnings Test the tester. Touch the probe of a continuity tester to its tip; it should light if the battery and its own connections are working. Never remove a thermostat or any electrical device until you have shut off the power to the Circuit. Always double-check that power is really off by testing all the wires in an outlet box. What Signs Should You Look For In Determining Your Furnace & Thermostat Types Determine the following: •What kind of heating/cooling system do I have? 1) Gas Furnace System 2) Boiler and Oil Fired Systems 3) Electric Heat and Cooling Systems 4) Heat Pump Systems • How many wires are running to my thermostat? • What is the Voltage? • Any other specific features A Millivoltage Gas Furnace System Will Have: 750 mV voltage and 2 thermostat wires Other specific features include: Gravity wall (room) furnace; direct or top vent wall furnace for small areas; mobile home direct vent wall furnace A Low Voltage Gas Furnace Systems Will Have: 24 Volts AC A standing pilot An electronic ignition 2, or possibly even 3, thermostat wires and if Air Conditioning is also on your system, then 4 or 5 wires Other specific features include: Intermittent pilot or hot surface ignition, forced air furnace Gas Fired Boiler Systems Will Have: 24 Volts AC Low Voltage 2 or 3 Thermostat wires Other Specific features include: Hot water boiler for radiant heat or baseboard hydronic systems Oil Fired Boiler Systems Will Have: 24 Volts AC or 120 Volts AC Low or High Voltage 2 or 3 Thermostat wires Other Specific features include: Hot water boiler for radiant heat or baseboard hydronic systems Electric Boiler Systems will Have: 24 Volts AC Low Voltage 2 or 3 thermostat wires Other specific features include: Hot water boiler for radiant heat or baseboard hydronic systems Oil Fired Furnace Systems will have: 24 Volts AC -Low Voltage 2 thermostat wires but if you also have air conditioning, it is 4 or 5 Other specific features include: Forced air furnace Electric Heat And Cooling Systems will have: ( *** This includes Low or high voltage systems for Electric Furnaces) 24 Volts 2 thermostat wires or if your unit also has air conditioning, it will be 4 or 5 Other specific features include: Forced air furnace Electric Air Conditioning Will Have: 24 Volts AC 4 or 5 thermostat wires Other specific features include: Outdoor condensing unit; cooling coils in furnace ductwork Electric Baseboard Heat will Have: 120 Volts AC or 240 Volts AC Either 2 or 4 thermostat wires Other specific features include: Localized heating with line voltage thermostat in each room Single Stage Heat Pump Systems Will Have: 24 Volt AC 4 or 5 thermostat wires Other specific features include: Outdoor heat pump unit providing heating and cooling Multi-Stage Heat Pump Systems will have: 24 Volt AC 7 or more thermostat wires Other specific features include: Outdoor heat pump unit providing heating and cooling Watch this video if your programable thermostat batteries died & you just want to do a 5 minute quick fix until you get new batteries at the store (just temporary) |
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