# Furnace is Hiccuping - Help Before it dies! **URL:** \ **Category:** Factual Questions\ **Created:** [January 20, 2013, 5:45am UTC](https://boards.straightdope.com/t/furnace-is-hiccuping-help-before-it-dies/647784 "2013-01-20T05:45:22Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [January 21, 2013, 1:29am UTC](https://boards.straightdope.com/t/furnace-is-hiccuping-help-before-it-dies/647784/21 "2013-01-21T01:29:19Z")
> [@usedtobe](#): > > I could dig out one of the relays I used when I was trying to salvage the original board and use it to switch on the inducer whenever there is a call for heat. but that would have it running for the duration of the burn. It looks to be a heavy-duty motor, but I don’t want to have it running 100’s times as long as designed. A)Inducer, not induction. Don’t know why, but I always get a kick out of it in these threads when the OP finally makes the move over to the word inducer. The type of motor used may be an induction type motor ( I think it is), but it induces a draft. It’s subtle and virtually everyone (myself included) says induction the first handful of times. B)The inducer runs the entire time the furnace is on. It’s what draws fresh air in, through the heat exchange and the exhausts it out to the outdoors. It it stops running during the cycle, one sensor or another will kick your furnace off. Anyways, the inducer motor comes on as soon as the T-stat calls for heat. It’s the first thing the control board does. It shuts off either when the t-stat tells the control board it’s satisfied or soon after that. I’m not totally sure what you’re trying to accomplish, but that’s when the inducer turns on and off. ---
**Author:** ![raindog](https://avatars.discourse-cdn.com/v4/letter/r/2bfe46/32.png) [@raindog](https://boards.straightdope.com/u/raindog)\ **Post date:** [January 21, 2013, 1:31am UTC](https://boards.straightdope.com/t/furnace-is-hiccuping-help-before-it-dies/647784/22 "2013-01-21T01:31:11Z")
> [@usedtobe](#): > > So far, it is either an intermittent connect from the t’stat or a bad relay - it goes click click click in rapid succession for 4-5 times, then will pause for a couple of seconds, then repeat the cycle. This time it caught on the second such cycle. > > My back and shoulder argue strongly against getting into it tonight. > > My notes from last time show red-to-green = call for heat - correct? I’ll do that short and see if it’s the relay or t’stat signal. > > I could dig out one of the relays I used when I was trying to salvage the original board and use it to switch on the inducer whenever there is a call for heat. but that would have it running for the duration of the burn. It looks to be a heavy-duty motor, but I don’t want to have it running 100’s times as long as designed. > > I’m just going to keep a jumper handy and short across the pressure switch if it fails completely. > I’m not up for tearing a furnace apart when temps are in the 30’s - 60’s (eat your hearts out, people with real weather). > > While we’re on HVAC: > > When the old board finally burned itself up, I looked it to see what all it was doing - and found a crystal - you don’t see those real often. I’m guessing it is used to create a square wave to match the flame sensor - correct? If not, what was it doing there? A couple things.. The inducer runs for the whole burn. If there is a call for heat, the inducer should be running in concert with the burners. In other words, the burners should **NEVER** be allowed to burn without the inducer running, for \*any \*length of time. I would never recommend jumping the pressure switch. Running the burners without the inducer gets unsafe immediately. Furnaces have gotten much smarter. The board isn’t satisfied seeing a closed pressure switch, because a faulty pressure switch that has failed closed could be dangerous. The furnace requires the switch to be open at the inception of a call for heat. The inducer starts and the switch closes. So…the board wants to "see’ the switch close. If the switch is already closed on a call for heat, the furnace won’t respond. ---
**Author:** ![raindog](https://avatars.discourse-cdn.com/v4/letter/r/2bfe46/32.png) [@raindog](https://boards.straightdope.com/u/raindog)\ **Post date:** [January 21, 2013, 1:37am UTC](https://boards.straightdope.com/t/furnace-is-hiccuping-help-before-it-dies/647784/23 "2013-01-21T01:37:12Z")
Red to white is a call for heat. ---
**Author:** ![gotpasswords](https://avatars.discourse-cdn.com/v4/letter/g/c57346/32.png) [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)\ **Post date:** [January 21, 2013, 1:53am UTC](https://boards.straightdope.com/t/furnace-is-hiccuping-help-before-it-dies/647784/24 "2013-01-21T01:53:01Z")
[QUOTE=raindog] …(although _most_ people accidentally replace stats that are fine. It is overwhelmingly not the stat that s the problem) [/QUOTE] How often do stats just go goofy? Our furnace was acting like the stack limit switch was tripping about a month ago. The stat would call for heat, the inducer starts up, followed by the gas valve opening, then the burner would run for a few minutes, then it would cut out, but the blower stayed on. Power-cycling the furnace would reset it and allow it to run for a while again. I called the landlord to say it was cold here (the joys of renting…) and the guy he sent out did about thirty seconds of visual troubleshooting, said the stat was bad and replaced it. Amazingly, he was right, as we haven’t had any trouble since then. Not knowing the intimate secrets of stats, it seems like the thing decided to short out internally, connecting R to G for a blower on call, and no amount of flipping the on/auto or heat/off switches would shut off the blower or restore heat. The original and replacement stats are very basic. No batteries or setback capacity, but as son as I have the extra bucks, I’m putting in a Nest. ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [January 21, 2013, 2:22am UTC](https://boards.straightdope.com/t/furnace-is-hiccuping-help-before-it-dies/647784/25 "2013-01-21T02:22:41Z")
> [@gotpasswords](#): > > The original and replacement stats are very basic. No batteries or setback capacity, but as son as I have the extra bucks, I’m putting in a Nest. I’ve been eying up the Nest system. I have a t-stat that I thought I would love. I bought it because it can, randomly, cycle the fan on and off to keep the temp in the house even. I was hoping to bring my AC bill down a bit. I haven’t used that feature in a while as I found a better way to bring my bill down and I get worried about shortening the life of my main blower. My system is programmable, but my days aren’t. Sometimes I get home at 3, sometimes I get home at 7, it’s always different and when I go to work I drop the temp pretty far. It takes about 45 minutes to bring it back up to comfortable. There’s other wifi systems out there as well, but this one just brought it back to my attention. It would be nice to say “Okay, I’m on my way home now” and pull up an app on my phone to kick the heat on. At least then it would have a 10 minute head start. Just remember. $250 programmable multistage Honeywell. Generic wifi system. Nest. $20 round gold thing with a dial. They’re all just glorified on/off switches. My big issue, the reason I put in an expensive t-stat with the circulator was that one room was really cold, all the time, no matter what I did. I finally tracked it down to drafty windows. My windows were put in in 1997. I bought my house in 2005. They should not have been drafty when they were less then 10 years old. From what I can tell, it has nothing to do with age or wear and tear, they’re just crappy, low end, contractor grade windows. Unfortunately, I don’t have thousands of dollars to replace them with good windows, so for now all I can do is listen to my furnace kick on and off every 10 minutes all winter. ---
**Author:** ![usedtobe](https://avatars.discourse-cdn.com/v4/letter/u/ec9cab/32.png) [@usedtobe](https://boards.straightdope.com/u/usedtobe)\ **Post date:** [January 21, 2013, 2:41am UTC](https://boards.straightdope.com/t/furnace-is-hiccuping-help-before-it-dies/647784/26 "2013-01-21T02:41:03Z")
> [@raindog](#): > > Red to white is a call for heat. So much for my careful notes from the last time… Does yellow go to red for A/C? I seem to remember that. It just went through a prolonged spasm trying to start - the LED’s never did anything other than flash in unison - I replaced the batteries in the t’stat. Turns out that the relay I heard was the t’stat. Trouble with them being so close. ---
**Author:** ![raindog](https://avatars.discourse-cdn.com/v4/letter/r/2bfe46/32.png) [@raindog](https://boards.straightdope.com/u/raindog)\ **Post date:** [January 21, 2013, 2:45am UTC](https://boards.straightdope.com/t/furnace-is-hiccuping-help-before-it-dies/647784/27 "2013-01-21T02:45:24Z")
> [@gotpasswords](#): > > How often do stats just go goofy? Our furnace was acting like the stack limit switch was tripping about a month ago. The stat would call for heat, the inducer starts up, followed by the gas valve opening, then the burner would run for a few minutes, then it would cut out, but the blower stayed on. Power-cycling the furnace would reset it and allow it to run for a while again. > > I called the landlord to say it was cold here (the joys of renting…) and the guy he sent out did about thirty seconds of visual troubleshooting, said the stat was bad and replaced it. Amazingly, he was right, as we haven’t had any trouble since then. > > Not knowing the intimate secrets of stats, it seems like the thing decided to short out internally, connecting R to G for a blower on call, and no amount of flipping the on/auto or heat/off switches would shut off the blower or restore heat. > > The original and replacement stats are very basic. No batteries or setback capacity, but as son as I have the extra bucks, I’m putting in a Nest. I dunno, but even a blind squirrel finds a nut from time to time. 😃 I don’t have enough information, and of course I wasn’t there, but based on what you’re describing the stat wouldn’t have been one of the first 7 or 8 things I looked at, if at all. And I couldn’t have troubleshooted that visually in 30 seconds. Replacing stats is exceptionally common with homeowners and inexperienced/ unqualified guys. _Exceptionally common._ _I can’t tell you how many_ calls I’ve been on where I’ve been called after a trip to Home Depot and a new stat installed—and the unit is doing the same thing as before. My guess? The stat was a coincidence and the unit failure fixed itself, and it just looks like the stat was the issue, or; he got lucky, or; he’s really, really good. _Really good._ (and he might be. I’m not dissing him) ---
**Author:** ![raindog](https://avatars.discourse-cdn.com/v4/letter/r/2bfe46/32.png) [@raindog](https://boards.straightdope.com/u/raindog)\ **Post date:** [January 21, 2013, 2:47am UTC](https://boards.straightdope.com/t/furnace-is-hiccuping-help-before-it-dies/647784/28 "2013-01-21T02:47:12Z")
> [@usedtobe](#): > > So much for my careful notes from the last time… > > Does yellow go to red for A/C? I seem to remember that. > > It just went through a prolonged spasm trying to start - the LED’s never did anything other than flash in unison - I replaced the batteries in the t’stat. Turns out that the relay I heard was the t’stat. Trouble with them being so close. Yes. On a call for A/C the calls are R to Y, _and_ R to G. Y being the compressor, and G being the fan ---
**Author:** ![usedtobe](https://avatars.discourse-cdn.com/v4/letter/u/ec9cab/32.png) [@usedtobe](https://boards.straightdope.com/u/usedtobe)\ **Post date:** [January 21, 2013, 2:47am UTC](https://boards.straightdope.com/t/furnace-is-hiccuping-help-before-it-dies/647784/29 "2013-01-21T02:47:57Z")
> [@Joey\_P](#): > > … so for now all I can do is listen to my furnace kick on and off every 10 minutes all winter. Maybe pass out heavy sweaters and drop the temp? I wear my bathrobe around the house - this thing has little or no insulation and trying to raise the temp 30 degrees is asking it to run continuously. Try dialing the temp down 1 degree - you will find the system’s “comfort zone” - a point past which the cost of each additional degree shoots up. ---
**Author:** ![gotpasswords](https://avatars.discourse-cdn.com/v4/letter/g/c57346/32.png) [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)\ **Post date:** [January 21, 2013, 3:31am UTC](https://boards.straightdope.com/t/furnace-is-hiccuping-help-before-it-dies/647784/30 "2013-01-21T03:31:04Z")
[QUOTE=raindog] My guess? The stat was a coincidence and the unit failure fixed itself, and it just looks like the stat was the issue, or; he got lucky, or; he’s really, really good. _Really good._ (and he might be. I’m not dissing him) [/QUOTE] I think he’s a blind squirrel. This is the same guy who when presented with a non-running air conditioner last summer immediately launched into adding more refrigerant without bothering to check subcooling or superheat after replacing a failed compressor motor cap. :rolleyes: To his credit, the cap was visibly bad, but unless he’s some sort of Jedi Master air conditioner whisperer, I’m suspicious of his abilities. 😛 ---
**Author:** ![usedtobe](https://avatars.discourse-cdn.com/v4/letter/u/ec9cab/32.png) [@usedtobe](https://boards.straightdope.com/u/usedtobe)\ **Post date:** [January 22, 2013, 9:32am UTC](https://boards.straightdope.com/t/furnace-is-hiccuping-help-before-it-dies/647784/31 "2013-01-22T09:32:05Z")
OK - It’s a t’stat problem. If I take a jumper across the thermostat terminals it works fine - so there is no loose wire causing intermittent start/stop. I have another t’stat which I swapped in - it clicks, but does nothing as to turning on the furnace - not even the inducer. Re-installed the first - back to the start/stop - but it is taking longer to finally catch. The blower switch on the t’stat works properly - it is just the call for heat that is screwing up. Is it even possible that the furnace has some level of resistance which is met by a jumper but not by the circuit on a thermostat? One t’stat acting up is one thing - for the second to not only act up, but to do even less seems a bit odd. I still have the toggle switch I rigged for A/C all those years ago - but switching a toggle to get heat off and on all day and night is not a welcome idea. ---
**Author:** ![raindog](https://avatars.discourse-cdn.com/v4/letter/r/2bfe46/32.png) [@raindog](https://boards.straightdope.com/u/raindog)\ **Post date:** [January 22, 2013, 12:08pm UTC](https://boards.straightdope.com/t/furnace-is-hiccuping-help-before-it-dies/647784/32 "2013-01-22T12:08:46Z")
> [@usedtobe](#): > > OK - It’s a t’stat problem. > If I take a jumper across the thermostat terminals it works fine - so there is no loose wire causing intermittent start/stop. > I have another t’stat which I swapped in - it clicks, but does nothing as to turning on the furnace - not even the inducer. > Re-installed the first - back to the start/stop - but it is taking longer to finally catch. > The blower switch on the t’stat works properly - it is just the call for heat that is screwing up. > > Is it even possible that the furnace has some level of resistance which is met by a jumper but not by the circuit on a thermostat? One t’stat acting up is one thing - for the second to not only act up, but to do even less seems a bit odd. > > I still have the toggle switch I rigged for A/C all those years ago - but switching a toggle to get heat off and on all day and night is not a welcome idea. Depending on the age of the stats, it might be the stat[s], but I’m loathe to condemn one stat, let alone two. They’re usually not bad. If it’s a new stat, it may not be configured incorrectly. If it’s configured for a heat pump, the delay is the stat waiting for second stage, the point in which the W terminal is energized. if it works right 100% of the time with a jumper _at the stat location_, (_100%_ of the time), but not with the stat, I’m probably condemning the stat. But it sounds a little weird. ---
**Author:** ![BlinkingDuck](https://avatars.discourse-cdn.com/v4/letter/b/eada6e/32.png) [@BlinkingDuck](https://boards.straightdope.com/u/BlinkingDuck)\ **Post date:** [January 22, 2013, 8:42pm UTC](https://boards.straightdope.com/t/furnace-is-hiccuping-help-before-it-dies/647784/33 "2013-01-22T20:42:00Z")
> [@usedtobe](#): > > Raindog talked me through replacing the guts of my furnace a few years back, for which I will be eternally grateful. > Now, we have another issue with the aging box. > > Lennox Elite natural gas updraft. > > The little motor which checks for a clogged flue is starting, stopping, starting again. > > About 3 times before the burners kick in. > > Is this more likely a clogged flue (we have had nasty storms lately, but I removed most of the trees around the house, so there aren’t any large limbs to hit it or deposit part of itself) or a defective motor or vacuum switch? > > Is there a way to clear a flue without getting on top of the house? Between weather and a bad back, am not looking forward. > > And, as always, money precludes the easy way of calling somebody, pointing to the box and saying “fix it”. Damn, I miss the days when that was all there was to it. > > I replaced the entire circuit board (this is an early model when everything is on a single board), so it shouldn’t be the cute toy relays this time. I know this is basic and probably not the problem, but have you checked and/or replaced your filter recently? I ‘fixed’ 2 people’s furnaces this winter by replacing their filter. They think I am som esort of HVAC demigod when I actually no next to nothing about it 🙂 ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [January 22, 2013, 9:51pm UTC](https://boards.straightdope.com/t/furnace-is-hiccuping-help-before-it-dies/647784/34 "2013-01-22T21:51:47Z")
> [@BlinkingDuck](#): > > I know this is basic and probably not the problem, but have you checked and/or replaced your filter recently? I ‘fixed’ 2 people’s furnaces this winter by replacing their filter. They think I am som esort of HVAC demigod when I actually no next to nothing about it 🙂 A clogged filter or condenser coil would slow down air flow, cause heat to build up, trip the limit switch and shut the entire unit down…but this would happen after the entire unit has come online and been running for a bit. The problem the OP is describing is that his furnace is quitting after only the inducer is running. At this point the filter doesn’t have any air moving through it yet. ---
**Author:** ![usedtobe](https://avatars.discourse-cdn.com/v4/letter/u/ec9cab/32.png) [@usedtobe](https://boards.straightdope.com/u/usedtobe)\ **Post date:** [January 22, 2013, 10:12pm UTC](https://boards.straightdope.com/t/furnace-is-hiccuping-help-before-it-dies/647784/35 "2013-01-22T22:12:31Z")
Jumper works 100% - every time The unaided t’stat just worked properly for a change - came on and stayed on. The t’stat configuration has not changed - it has two tiny switches - a ELEC/GAS slider and a push-button “reset” (presumably for the programming). My roomie won’t touch anything, and I didn’t so much as remove the cover of the t’stat before it started this bit. Maybe we can replace the “blind squirrel/nut” expression with “every once in a while it IS the thermostat” 😃 ---
**Author:** ![usedtobe](https://avatars.discourse-cdn.com/v4/letter/u/ec9cab/32.png) [@usedtobe](https://boards.straightdope.com/u/usedtobe)\ **Post date:** [January 22, 2013, 10:15pm UTC](https://boards.straightdope.com/t/furnace-is-hiccuping-help-before-it-dies/647784/36 "2013-01-22T22:15:31Z")
Oh - in addition to this happening WAY upstream from “clogged filter”, we can rule that out - this house is so cheaply built, it does even HAVE a filter. Think of all the money I’m saving by not having to replace a filter element! ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [January 22, 2013, 10:26pm UTC](https://boards.straightdope.com/t/furnace-is-hiccuping-help-before-it-dies/647784/37 "2013-01-22T22:26:24Z")
> [@usedtobe](#): > > Oh - in addition to this happening WAY upstream from “clogged filter”, we can rule that out - this house is so cheaply built, it does even HAVE a filter. > Think of all the money I’m saving by not having to replace a filter element! When your AC stops working the answer is going to be “because you don’t have a filter so the coils are clogged and the low air flow caused them to ice up”. ---
**Author:** ![raindog](https://avatars.discourse-cdn.com/v4/letter/r/2bfe46/32.png) [@raindog](https://boards.straightdope.com/u/raindog)\ **Post date:** [January 22, 2013, 11:20pm UTC](https://boards.straightdope.com/t/furnace-is-hiccuping-help-before-it-dies/647784/38 "2013-01-22T23:20:05Z")
> [@usedtobe](#): > > Jumper works 100% - every time > The unaided t’stat just worked properly for a change - came on and stayed on. > > The t’stat configuration has not changed - it has two tiny switches - a ELEC/GAS slider and a push-button “reset” (presumably for the programming). > > My roomie won’t touch anything, and I didn’t so much as remove the cover of the t’stat before it started this bit. > > Maybe we can replace the “blind squirrel/nut” expression with “every once in a while it IS the thermostat” 😃 LOL Maybe it _is_ the thermostat. A little background… It _is_ the thermostat enough of the time that I have 4 different models on my truck. Stats \*do \*go bad, and they get replaced. The back story is that the stat gets accused 50 or 100 times for every time it’s actually guilty. Homeowners of all stripes, _and_ inexperienced HVAC guys want to replace the stat. It’s entirely logical; it’s the one thing you can see and manipulate. If you turn to heat or A/C and it doesn’t respond, your brain logically thinks: It’s not doing what I told it to do. So…Many times every year I see brand spanking new stats on the wall that represent somebody’s logical guess as to what’s wrong. And, of course, if I’m there it’s because the guess was wrong. Even among customers who don’t replace the stat first (and that would be most of them) it’s rarely the stat. In the summer I’ll replace 3 bad stats. I’ll replace 50 bad capacitors alone. Same with heating. I’ll replace 1 or 2 stats, and 40 ignitors, and clean countless flame sensors. So maybe it was the stat and it’s licked. Yiippeee. ---
**Author:** ![usedtobe](https://avatars.discourse-cdn.com/v4/letter/u/ec9cab/32.png) [@usedtobe](https://boards.straightdope.com/u/usedtobe)\ **Post date:** [January 23, 2013, 2:50am UTC](https://boards.straightdope.com/t/furnace-is-hiccuping-help-before-it-dies/647784/39 "2013-01-23T02:50:07Z")
> [@Joey\_P](#): > > When your AC stops working the answer is going to be “because you don’t have a filter so the coils are clogged and the low air flow caused them to ice up”. Spoil Sport 😛 ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [January 23, 2013, 3:14am UTC](https://boards.straightdope.com/t/furnace-is-hiccuping-help-before-it-dies/647784/40 "2013-01-23T03:14:33Z")
> [@usedtobe](#): > > Spoil Sport 😛 Well, when your AC does stop working in the dead of summer on a hot humid day, the first thing I want you to do is set the switch that says COOL-OFF-HEAT to OFF and the fan switch to ON and let that run for about an hour. If water comes dripping out of the evaporator tube (above the furnace) and the AC works again, the first thing we’ll need to look at (since you don’t have a filter) is cleaning the coils. There’s probably an access panel in the plenum and something [like](http://www.stoveparts.net/Merchant2/graphics/00000003/UFC1.jpg) this makes it a much easier job. Don’t bend the coils/fins and don’t cut your knuckles on the coils or arms on the sheet metal. [Previous page](https://boards.straightdope.com/t/furnace-is-hiccuping-help-before-it-dies/647784.md?page=1) [Next page](https://boards.straightdope.com/t/furnace-is-hiccuping-help-before-it-dies/647784.md?page=3)