Great video. I just moved into a house built in the 80's and it has these thermostats. I've been working on the boiler and I was thinking about upgrading the thermostats but after watching this video I've decided to stick with the original mercury switch units. I like knowing what's going on inside and now I do thanks to this video. This is one of the most clear presentations of a relatively complex subject that I have ever seen on RU-vid.
My buddy and I are trying to fix the AC in a new house we’re renting and came across this, this had nothing to do with the real issue but it was still cool lol, good video👍
I was wondering how my Honeywell thermostat worked for my wood stove fan and this tutorial was SO helpful!! Thank you for the video, I really enjoyed the lesson!
EXCELLENT tutorial. I hope you teach for a living, because you have talent for explaining things. ( I am a very old electronic tech who never before learned how these work.)
What does "Longer" mean on the rheostat scale? Further, what do the numbers mean? Are they temp degrees? My boiler is cycling on and off every 2 minutes near set point. I'd rather have a larger temp swing and less wear and tear on the gas valve. Which way should I move the pointer? Thanks for this video!
Thank you for your great explanation. Your video allowed me to understand and trouble shoot my thermostat problem and know how to set up my replacement, which was one that I had kept from another room when I changed to a digital one years ago. - Blessings
Actually the rheostat _is_ the heating element. All a heating element is, is a resistor that is designed to tolerate getting hot. In this case, the amount of heating is fairly modest (a watt or so at most). The copper thing is merely a conductor that is part of the circuit.
Hi, thanks for this. I think had a that correction as an annotation on the video, but RU-vid removed the annotations feature, so all the post-filming corrections I added to my videos are now lost.
Converted from oil to gas and the installer said I could not keep the fantastic honeywell round. He obviously knew nothing about the heat anticipator adjustment. You set it long for hot water heat, medium for the heavy heat exchangers in oil furnaces, and near zero for gas furnaces with their tiny heat exchangers. I adjusted mine. Saved much money on a new one built to fail. Has worked perfectly since. Should last for 100 years, as it is designed to do.
Old reliable Mercry sw is the best. Have had 2 digitals in my life, and both went to junk. Reinstalled the mercury ones, system works perfectly. My mothers old furnace was replaced yrs ago, and the serviceman told her she couldn't keep her old Honeywell. They took it, and am sure are using it in their own way.
I had the same thing happen to me. The tech replaced my old mercury Honeywell T87 with a piece of crap digital Honeywell T87, and took the mercury thermostat with him. Now, I'm replacing that one with a new, unused mercury Honeywell T87 I found on eBay.
Helpp we had to take out a wall and my husband decided for some dumb reason to take apart This and now our furnace won’t stop running and is stuck at 80
I think the mercury switch sends 24V from R to W and G if heat is on and Y and G if cooling is on. My furnace has had this thermostat as far back as I can remember. It could possibly be 38 years old like the furnace. It had started short cycling so I got to looking into it. Cleaned all the dust out of it and fired the furnace back up and lo and behold the variable resistor smoked and burned. I suppose a fixed resistor or other form of variable resistor would fix itbut not sure its worth the risk. I will definitely be putting a fuse on the 24V system after this. Luckily I was standing there looking at it and got it shut back down before it really fried. What it did was burn all the shielding off 6 or 7 turns of the magnet wire close to the sliding contactor.
Where do you stick the arrow thing at? My furnace keeps running shutting off couple mins then turning off. It's getting too hot in my house. And I have the same exact thremsot
Hi. Great video! Do you think there is any way to adjust the thermometer on an older T86A7 with the smaller dial? There's no way to access nor adjust the thermometer "spring" thing.... The back, beneath the mount plate only shows like the end of the metal dial shaft embedded in the plastic but with a manufacturer's non-tamper goo-seal across it... (and other items on its front.) I mean, I'm a really mechanically minded fellow and I can't see any way to remove that dial / knob... The thermometer is sluggish and off by about 7 degrees F above other thermometers, here. (including a Honeywell that looks like yours with the easy access adjusting screw on its back...) But, the T86A7 has no access whatsoever... A pity because its a gorgeous little piece. I only use these classic thermostats around the house as thermometers only and are not hooked up. Thanks...
I have a simple question: There is a basic Honeywell heat-only round in my apartment hallway. It looks to be less than ten years old, and has no exterior switches. It controls the heat to our hot-water radiators. Even when the set point is 72-74° F, it heats only to 68°. The unit appears to be installed level, and I’d like to check the heat anticipator setting inside. So please tell me: HOW the HECK to get inside this thing and check the anticipator setting? I don’t want to yank on something and break the thermostat like a buffoon!
This is a great "how it works," but mine actually works, though with some difficulty. One night, meaning to turn it all the way off, I turned it too far, I felt some break, and now the whole dial assembly slips on its shaft, so that the "Honeywell" logo is no longer level. I have to overturn it the other way to straighten it. At the same, it resists efforts to pull it off the shaft so I can see what's going on, and I don't want to force it. Anyone familiar with this problem? Also, I second the comment below by Stephanie Smith. How do you get this thing apart and/or remove and replace it?
I move it all the way to the right and the rooms are not hot enough, could be that thermostat is not working properly ? Any advice ? Thanks for the video.
Enjoyed your video. I have a Honeywell T87F Round. This is similar to the thermostat in your video. Quick question: How did you remove the clear face cover? My degrees are off on the top needle adjustment and lower room temperature. Both readings are off by 4 degrees. I am thinking if I could rotate the dial with numbers then this would resolve my issue. Please and thanks. Alex Taft
Hi I have one of those thermostat want to put it in my garage I have a red green an white wire but that thermostat has two spots witch wire goes there thanks
The sad truth is no. That's a second, heavier-duty thermostat which is attached to your actual furnace. It is also operated by a bimetal penetrates the heat duct from the outside and starts the blower one minute fan before ignition and and shuts if off about a minute after the flame goes out, to make sure the that heat does get to build up with no fan running. I know this because mine failed and now the fan is on all the time unless I go down to the basement and power down the whole thing. Regarding your problem, it's probably with your igniter.
I have this in my apartment and I’m unable to figure out how to turn the thermostat on cool. I don’t see a system mode button etc. I’m unable to move to the bottom part of the thermostat.
Fascinating! What's the resistance of the rheostat? I've experimented with shorting the terminals and got about 300mA. I'm guessing the rheostat also serves as a protective resistor in case of a short?..
I have a Honeywell round thermostat, although it's not one of the classics with that uses mercury (I was hoping it was because I wouldn't have needed to look up how to calibrate that one). Instead I have a classic Honeywell round thermostat that has circuit boards. Conclusion: We can't assume round thermostats don't operate using 21st technology.
The new Honeywell Round has a lithium button battery squirreled away on its circuit board. Its NOT easy to get at, but it is replaceable. That means the design expects you to replace the thermostat every 10 years - unless you are relatively geeky - (as well as replace all the broken pipes in the garage you had set to 45 degrees which froze the pipes when the lithium battery died). That's modern engineering for you. Kick the can down the road 10 years and who cares after that.
@Blondie SL it has a fan on and auto option on the thermostat which sends 24 volts through the g(fan) terminal on the thermostat to the g terminal on the circuit board in the furnace then it sends 120 volts to blower motor so yes it can control the blower motor in the furnace
The old mercury and magnetic thermostats lasted for ever .....these only a few years if that and go caflewy......installed these in my sons house my house and a rental....all do not last..........the one shown here is obsolete.....no replacement metal .....in there bub....thermistor.....and electronics.......
Enjoyed your video. I have a Honeywell T87F Round. This is similar to the thermostat in your video. Quick question: How did you remove the clear face cover? My degrees are off on the top needle adjustment and lower room temperature. Both readings are off by 4 degrees. I am thinking if I could rotate the dial with numbers then this would resolve my issue. Please and thanks. Alex Taft
No, just make sure the thermo is level, if it is, slightly turn it and replace the mounting screws, experiment until the temp is where you want it. Do not take the thermostat face apart.
