Flyinfool Posted December 30, 2018 Share #1 Posted December 30, 2018 (edited) I know we have a few HVAC folk around here. It is getting a bit chilly at times around here. I think I might have 2 unrelated issues happening at the same time which is helping to keep me confused. The patient is a 30 year old Tempstar. Model #867 .769423, on natural gas. The symptoms are. 1. Forced air blower will not shut off. It just keeps blowing cold air. If the thermostat asks for more heat while the blower is on it will light the pilot light but not the main burner, and just keep blowing cold air. I have pulled out the blower switch to see if it might be dirty but it is not and all of the switches move and open and close as they should. while it is blowing the cold air the contacts are staying closed keeping the fan on. A wack with the handle of a screwdriver (technical tap) will open the switch contacts, which shuts off the fan and opens the gas valve to the main burner and normal function is restored for a few hours. 2. The main burner does not want to light. The pilot is lighting (electronic ignition for the pilot) I checked for power to the main burner gas valve and there is no power going to it to tell it to open. BUT all it takes is a tiny puff of air directed at the pilot, or even just a wave of my hand to move some air toward the pilot and the power to the gas valve immediately comes on and the main burner lights and then the rest of the cycle is normal, unless the blower forgets to shut off at the end of the cycle. All this without actually touching the furnace, just the tiniest puff of air will trigger it. My guesses, 1. The air control switch is on its way out, and may need to be replaced. about $110 2 screws and 6 wires, should be a 10 minute job. I just hate to take a $120 shot in the dark. 2. The pilot sensor is bad or dirty. I can not see it without significant disassembly. I am thinking that the small puff of air is just enough to push the pilot over a bit so that it heats the last couple of degrees needed to trigger the sensor. Could be a dirty sensor or dirt around the orifice for the pilot making the flame the wrong shape. or it could be the sensor on its way out. The other thought, I did have to replace the inducer last winter. I sure does not sound like it is turning 3400 rpm. It used to make a lot more noise than it does now. I am not sure how to get in there to actually measure the speed. I hope it is not that, not only was it rather expensive, but I had a hard time finding someone that actually had one in stock. Again it is $110 for a new pilot burner and sensor assembly and $222 for the module that controls the gas valves. I hate throwing money at a problem. I was planning to replace the furnace the summer of 2020. Edited December 30, 2018 by Flyinfool Link to comment Share on other sites More sharing options...
cimmer Posted December 30, 2018 Share #2 Posted December 30, 2018 how about the thermo coupler or flame sensor being carboned up a bit. Try taking some emery cloth to it and polish it clean. I would do that to my old furnace at the start of the season and it would have no issue. When I forgot to then I would have lighting issue with the main burners. not sure on the fan blower issue but I think you are looking at the correct item.. I had to replace my 24 year old furnace as the control board died on it and was no longer available and the recommended replacement was $1,000 to rewire it in to work.. I just went with a new furnace as you know how important they are up here in the cold north. Good luck.. Rick F. Link to comment Share on other sites More sharing options...
ragtop69gs Posted December 30, 2018 Share #3 Posted December 30, 2018 I have no diagnostic suggestions but I've been told by several HVAC tech's to never use ANY type of sandpaper on the thermocouple/ flame sensor, just use a dollar bill to clean them, they are just abrasive enough to to the job without harming the part. Sent from my SM-N920V using Tapatalk Link to comment Share on other sites More sharing options...
RDawson Posted December 30, 2018 Share #4 Posted December 30, 2018 I did the commercial/industrial HVAC thing for 13 years before I started fighting fires. I'm not familiar with Tempstar but the units we were seeing 30 years ago were at the beginning of the energy conservation kick. The lighter weight heat exchangers didn't hold up well at all. The reason I say that is I would inspect the exchanger before spending any $$$ on it. If it has the older inducer instead of the negative pressure ones used today a bad exchanger can cause you to wake up dead. If I remember correctly the indoor fans on most of those older units operated on a heat button switch mounted near the exchanger. It sounds like you're on the right track on the pilot sensor to me too. 30 year old memories along with my CRS may be totally off :puzzled: 🤷*♂️🤷*♂️🤷*♂️ Yeah I know after proof reading this I'm not much help. Link to comment Share on other sites More sharing options...
Vickersguy Posted December 30, 2018 Share #5 Posted December 30, 2018 Sounds like the condensing furnace I had in the late 80's. As I remember its a bear to work on. I had a similar or exactly the same issue with mine. (it's been a long time ) I recollect that the pilot flame was too far away from the thermocouple. I had to tweek the thing so the flame hit the thermocouple as it was only close to the tip. I also had issues with the exhaust blower not making the switch. If you have a power exhaust blower, that has to make the switch to light the main burner... but that shouldn't be affected just by moving air close to the furnace. I'm voting for the flame not being close enough to the thermocouple. The thermocouple should be secured with a nut you can loosen, then slide the thermocouple in a bit so it's closer to the pilot. Then take two shots of whiskey and call me in the morning. Link to comment Share on other sites More sharing options...
Vickersguy Posted December 30, 2018 Share #6 Posted December 30, 2018 On reading your post carefully, You may have several problems. If there is a hole in your heat exchanger, that could be messing up the natural draft and pushing the pilot flame away from the thermocouple. You must be cautious about that. It would be worth the effort to use a smoke source, like incense or a cigarette, to check the air flow around the pilot while the blower is running but the main flame is not lit. If air is flowing out of the combustion side of the heat exchanger you should see the smoke blowing away from the pilot area, towards your hand holding the smoke source. This would indicate you have a hole in the heat exchanger. If the smoke rolls gently into the furnace, while the blower is running, you're good. If you have a standard fan controller, which looks like a silver box on the front of the furnace with a shielded bi-metallic curley Q extending into the heat exchanger, it probably has reached the end of it's service life at 30 years. When they get corroded, they don't twist when heated and throw the fan switch like they should. You might adjust the "off limit', higher. It's one of the little silver "clock hands" around the disc inside the box. ( I hope I've got this right, Clockwise from "noon" the first hand is the emergency shut off switch that shuts off the burner to prevent heat exchanger damage when the blower fails to run. Second hand is the "on" switch to start the blower, and the third hand is the "off" switch that turns the blower off. ) Moving the third hand a short distance counter clockwise, will raise the temp the fan will shut off at and will compensate for the lack of travel that might be the problem with the fan switch. I'm thinking that the fan switch not shutting off, is it's own problem and not connected to the main flame ignition issue, unless there is the fore mentioned hole in the heat exchanger. You probably know all this stuff already, but I thought it would be best to examine the basics first before the more exotic explanations. Link to comment Share on other sites More sharing options...
uncledj Posted December 30, 2018 Share #7 Posted December 30, 2018 As far as the pilot is concerned, doesn't sound like a thermocouple, but rather a flame sensor, which is nothing more than a steel rod that will conduct a tiny bit of electricity to ground through the flame. (flame rectification) It'd be a good idea to clean it...like someone said, no sandcloth...small wire brush or scotch brite pad. The idea there is that sandcloth has silicates in it which will imbed in the steel while cleaning, and when heated can melt into the steel thereby insulating it from the flame. So....no sandpaper. It shouldn't be that tough to pull the pilot ignitor / flame sensor as an assembly, and while you're at it, if you have compressed air, blow out the pilot orifice. They sometimes get restricted and a small pilot flame can cause that issue as well. Keep in mind that with flame rectification, unlike a thermocouple, the flame sensing is instant. It doesn't need to heat up....the flame merely has to contact the sensing rod and it'll go to main flame. As far as the fan switch goes, best to post a pic of it before speculating further. Link to comment Share on other sites More sharing options...
Freebird Posted December 30, 2018 Share #8 Posted December 30, 2018 Is there an air intake from outside the house? I had a similar problem with my furnace a few years ago. There is a differential pressure switch that will keep the gas valve from opening. Mine has a duct, something like you see your a clothes dryer, that draws in air from outside the house. Yellow jackets had built a nest at the intake on the outside wall of the house. I cleaned it out and all was good. Link to comment Share on other sites More sharing options...
M61A1MECH Posted December 30, 2018 Share #9 Posted December 30, 2018 Well I was going to say something smart like , move to Florida we do not need furnaces, most of the time, but figured that would not be helpful, so I did not say that. Link to comment Share on other sites More sharing options...
RDawson Posted December 30, 2018 Share #10 Posted December 30, 2018 For the good news get ready for the sticker shock of new units. In the ever lasting search for higher efficiency and free energy heat exchangers have gotten paper thin, coils are aluminum and thin, the new ozone saving refrigerants run at ungodly headpressures, motors are computer controlled multi speed units fit for space travel. With $1000 motors, blown coils and lines, burned out exchangers, and fried circuit boards you can expect 10-12 years service from a unit that costs double to buy and a fortune to maintain. But hey you save $150 a year in energy. I want my old units back with cast exchangers and solid state controls. 30 years of service with cheap repairs, I'll gladly pay for the wasted energy. I don't need a 14 speed condensor motor anyway. Sure am glad the tree huggers can enjoy their $10 lattes while basking in the glow of saving the world with energy savings. Now go see how much energy is used to make new units to replace these pieces of *+=\\.|{}#. :soapbox::bang head: Link to comment Share on other sites More sharing options...
Flyinfool Posted December 30, 2018 Author Share #11 Posted December 30, 2018 This furnace is one of the early high efficiency ones, I think it was listed as 95%. It has the PVC exhaust but still uses inside air for combustion. Here is a pic of the blower switch. it is p/n 1002743. I did pull out my blower switch and it was nice and clean. I did try bumping up the shut off temp by 5 degrees and that made no difference. the no fan overheat part of the switch is factory set to be 30 degrees above the fan start/stop setting. The plan for today is to pull the burner assy to get at the pilot and see if cleaning it up will help. I will pull some panels to see if I can get to the heat exchanger to check for holes. Because it is an old furnace and It has had the heat exchanger replaced 6 times already I do have CO detectors all over the house including one in the duct work to hopefully avoid the waking up dead part. If it will cost more than $200 to fix this thing I will have to bite the bullet and start furnace shopping now. I did a bit of looking and I can get a 98% efficient one for $1900, I would have to do my own install. I have no problem with the electrical hookups, the PVC intake and exhaust work or the gas line. It is only the modifications to the duct work that I do not have technology for. Maybe I need to add a sheet metal brake to my shop as part of the cost..... Part of the problem with the install is that I want to move the furnace location over about 6 feet so there will be a bunch of duct work involved. And of course I will also have to move a cold water pipe out of the way which could end up having to replumb the entire cold water side of the house...... Link to comment Share on other sites More sharing options...
uncledj Posted December 30, 2018 Share #12 Posted December 30, 2018 For the good news get ready for the sticker shock of new units. In the ever lasting search for higher efficiency and free energy heat exchangers have gotten paper thin, coils are aluminum and thin, the new ozone saving refrigerants run at ungodly headpressures, motors are computer controlled multi speed units fit for space travel. With $1000 motors, blown coils and lines, burned out exchangers, and fried circuit boards you can expect 10-12 years service from a unit that costs double to buy and a fortune to maintain. But hey you save $150 a year in energy. I want my old units back with cast exchangers and solid state controls. 30 years of service with cheap repairs, I'll gladly pay for the wasted energy. I don't need a 14 speed condensor motor anyway. Sure am glad the tree huggers can enjoy their $10 lattes while basking in the glow of saving the world with energy savings. Now go see how much energy is used to make new units to replace these pieces of *+=\\.|{}#. :soapbox::bang head: Well stated, but brother, you don't know the half of it. The constant pursuit of energy efficiency has caused more issues with reliability, functionality and service life than people realize. I do this stuff for a living (commercial / industrial) and see it every day. Keep it simple, stupid is more true today than ever. Trouble is that the gubment mandates this stuff without knowledge of or concern for unintended consequences or real world benefits / failings. Having said that, FlyinFool...don't get too enamoured with ultra high efficiency. Salespeople make it sound great, but it's not. Fan switch doesn't seem the type prone to failure, but may be....does the switch control the fan motor directly or through a relay? (Stuck / sticking relay?) Link to comment Share on other sites More sharing options...
videoarizona Posted December 30, 2018 Share #13 Posted December 30, 2018 (edited) I have no diagnostic suggestions but I've been told by several HVAC tech's to never use ANY type of sandpaper on the thermocouple/ flame sensor, just use a dollar bill to clean them, they are just abrasive enough to to the job without harming the part. Sent from my SM-N920V using Tapatalk I use a piece of notebook or printer paper. But that doesn't sound like Jeff's problem, unfortunately. Although it's worth a shot, Jeff. If the sensor rod sticking into the flame area doesn't sense flame...no burner. Clean by removing sensor rod...pull it through a piece of folded paper a few times. Don't put any side pressure as they are brittle side to side. If it isn't even trying to light, I'd go with pilot not hitting the main gas due to wrong air movement. Check the exchanger carefully. I like the using smoke...good reason to fire up a cigar! Grins! Edited December 30, 2018 by videoarizona Link to comment Share on other sites More sharing options...
uncledj Posted December 30, 2018 Share #14 Posted December 30, 2018 This furnace is one of the early high efficiency ones, I think it was listed as 95%. It has the PVC exhaust but still uses inside air for combustion. Here is a pic of the blower switch. it is p/n 1002743. https://www.venturerider.org/forum/attachment.php?attachmentid=115226 I did pull out my blower switch and it was nice and clean. I did try bumping up the shut off temp by 5 degrees and that made no difference. the no fan overheat part of the switch is factory set to be 30 degrees above the fan start/stop setting. The plan for today is to pull the burner assy to get at the pilot and see if cleaning it up will help. I will pull some panels to see if I can get to the heat exchanger to check for holes. Because it is an old furnace and It has had the heat exchanger replaced 6 times already I do have CO detectors all over the house including one in the duct work to hopefully avoid the waking up dead part. If it will cost more than $200 to fix this thing I will have to bite the bullet and start furnace shopping now. I did a bit of looking and I can get a 98% efficient one for $1900, I would have to do my own install. I have no problem with the electrical hookups, the PVC intake and exhaust work or the gas line. It is only the modifications to the duct work that I do not have technology for. Maybe I need to add a sheet metal brake to my shop as part of the cost..... Part of the problem with the install is that I want to move the furnace location over about 6 feet so there will be a bunch of duct work involved. And of course I will also have to move a cold water pipe out of the way which could end up having to replumb the entire cold water side of the house...... If anything, you'd want to DROP the shutoff temp a few degrees to help disperse any residual heat. Link to comment Share on other sites More sharing options...
cowpuc Posted December 30, 2018 Share #15 Posted December 30, 2018 ,,, WIN/WIN!!! When you need heat, just tap on the Blower switch to shut the motor off and wave your hand to move some air so the burner will light,,, easy peasy.. As cold as it gets around here, having to physically control the unit like that may keep you busy enough that your WWW plans for this winter will be set aside.. WIN/WIN... Sounds like that switch your tapping on is done.. Makes no sense that tapping on would seperate the contacts if they were being held in by a current flow. I would start there but,,, consider the source Link to comment Share on other sites More sharing options...
WildBill1 Posted December 30, 2018 Share #16 Posted December 30, 2018 Before you do a lot of disassembly check your condensate line and your pvc exhaust pipe for obstructions. Have had similar problem in the past with a different brand unit. Link to comment Share on other sites More sharing options...
Sylvester Posted December 30, 2018 Share #17 Posted December 30, 2018 I feel for you Fool and I have no expertise with HVAC, but maybe you will be preoccupied long enough that the white wash machine is dormant for a while. Hope the repair is quick and cheap. Link to comment Share on other sites More sharing options...
Flyinfool Posted December 30, 2018 Author Share #18 Posted December 30, 2018 You are all correct, this is keeping me away from the WWW, I just do not have time to go out and turn it off........ I got the pilot unit out and I think it was the problem, there is a flame shield that forces the flame over the flame sensor, Way back when the furnace was built, someone did not use a second wrench when they tightened the gas line to the orifice and twisted the flame shield about 30° so only the very edge of the flame was hitting the sensor. The sensor also had a good coat of carbon on it. I straightened out the flame shield and cleaned up the sensor with a folded piece of paper. Now when the pilot comes on the main burner lights instantly, or at least within a half second of the pilot coming on. It NEVER lit that fast in the 30 years I had it. It always took 3-5 seconds of pilot before main burner light. Along the same lines, the pilot is a pretty big flame, it is directly below the blower switch. I am wondering if the big 6 inch high pilot flame was just enough heat to turn the blower on?? Since I cleaned and realigned the pilot the blower has not hung either? So far the beast seems to be cycling normally. Link to comment Share on other sites More sharing options...
Sylvester Posted December 30, 2018 Share #19 Posted December 30, 2018 I am very pleased that you may have a remedy. And if all goes well then send the snow to the SE. I can handle it. :snow: Link to comment Share on other sites More sharing options...
Flyinfool Posted December 30, 2018 Author Share #20 Posted December 30, 2018 I am now in wait and see mode. If the blower goes back to not working correctly then I will be pretty confident that it is the switch. The switch is directly switching motor power, no relay. There is a relay but that just selects the blower speed. Either speed still goes thru the blower switch. My volt meter says that when the blower is on and should not be the switch is closed. This gives me time to work on diabolical devices in the basement while I monitor the furnace. Link to comment Share on other sites More sharing options...
frankd Posted December 31, 2018 Share #21 Posted December 31, 2018 Along the same lines, the pilot is a pretty big flame, it is directly below the blower switch. I am wondering if the big 6 inch high pilot flame was just enough heat to turn the blower on?? Since I cleaned and realigned the pilot the blower has not hung either? So far the beast seems to be cycling normally. Doesn't the pilot go out when the the thermostat is satisfied and the flame goes out? Frank Link to comment Share on other sites More sharing options...
uncledj Posted December 31, 2018 Share #22 Posted December 31, 2018 Along the same lines, the pilot is a pretty big flame, it is directly below the blower switch. I am wondering if the big 6 inch high pilot flame was just enough heat to turn the blower on?? Since I cleaned and realigned the pilot the blower has not hung either? So far the beast seems to be cycling normally. Doesn't the pilot go out when the the thermostat is satisfied and the flame goes out? Frank 6" is one helluva pilot flame..... I don't believe that Fool has a standing pilot...His merely lights the pilot as a step to bring on the main burner. Link to comment Share on other sites More sharing options...
Flyinfool Posted January 1, 2019 Author Share #23 Posted January 1, 2019 You are correct, the pilot goes off when the burner shuts down. Every time the blower was hung the thermostat was calling for heat, the pilot ligt was lit and the blower was running. So it may have been the pilot coming on, making just enough heat to turn on the fan and then just sitting in that state because the pilot was not hitting the flame sensor. Since my cleaning of the flame sensor and realignment of the pilot flame shield the furnace has not missed a beat. Link to comment Share on other sites More sharing options...
cowpuc Posted January 1, 2019 Share #24 Posted January 1, 2019 You are correct, the pilot goes off when the burner shuts down. Every time the blower was hung the thermostat was calling for heat, the pilot ligt was lit and the blower was running. So it may have been the pilot coming on, making just enough heat to turn on the fan and then just sitting in that state because the pilot was not hitting the flame sensor. Since my cleaning of the flame sensor and realignment of the pilot flame shield the furnace has not missed a beat. :dancefool::dancefool::dancefool::dancefool::dancefool::dancefool::dancefool: Ahhhhh,,, ought ohhhhh,, just checked the weather radar,,,, looks like your attention span being drawn away from the WWW didnt last long ya lop eared varmint .... Link to comment Share on other sites More sharing options...
Flyinfool Posted January 1, 2019 Author Share #25 Posted January 1, 2019 :dancefool::dancefool::dancefool::dancefool::dancefool::dancefool::dancefool: Ahhhhh,,, ought ohhhhh,, just checked the weather radar,,,, looks like your attention span being drawn away from the WWW didnt last long ya lop eared varmint .... WHAT??? Link to comment Share on other sites More sharing options...
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