# Furnace not always starting



## wacor

Anybody have a clue if I have a faulty igniter or thermostat or something else that is simple to check?

Have a typical forced air furnace with a White Rogers programable thermostat. Thermostat is set as follows: 6 am until 8:30 am the temp is set at 68 f. Then from 8:30 am until 4:00 pm the temp is at 62 f. From 4:30 pm until 11 pm the temp is back to 68 f. Then during the night the temp is back to 62 f.

About 4-5 times now when it called for the furnace to warm up the house to 68 f the furnace has not come on. I go down and turn the power switch on the furnace off and on a couple of times and then you can hear the igniter and the furnace fires right up and will continue to run just fine. Until at some point a day or two or more days later when it is time to warm the house back up the furnace is off.

Each time the furnace failed to start the thermostat indicator showed the furnace should be running. Each time the furnace failed to start the temperature in the house was not much lower than 62 f which tells me that the furnace had been running to keep up the minimum temperature in the colder settings.

On the weekends I set the furnace so that it is 68 f from 8:30 am until 11:00 pm and the furnace has always keep running during the day. Same goes at night during the week. The furnace never failed to start in the 68 f mode once you got it going after the first failed start. 

I am leaning towards it must be a thermostat problem but wonder why turning on and off the power switch would do anything to the thermostat. Seems like if this was a thermostat isssue then the furnace would fail to start occasionally during the warmer cycles which as I recall it never has. 

Anybody with an idea?

Thanks

Bill


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## JohnWill

You don't mention gas or oil, I'm assuming oil here.

One question. When it fails to warm up to 68 degrees, will if fall lower than 62 degrees? In other words, is the furnace turning on at all at any temperature? If not, then I'd suspect the furnace, otherwise I'd be looking at the thermostat. There is a high temperature thermostat on most oil furnaces that will prevent the furnace from firing if it's defective. Incorrectly setting the high limit thermostat will also cause this kind of issue.


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## wacor

JohnWill said:


> You don't mention gas or oil, I'm assuming oil here.
> 
> One question. When it fails to warm up to 68 degrees, will if fall lower than 62 degrees? In other words, is the furnace turning on at all at any temperature? If not, then I'd suspect the furnace, otherwise I'd be looking at the thermostat. There is a high temperature thermostat on most oil furnaces that will prevent the furnace from firing if it's defective. Incorrectly setting the high limit thermostat will also cause this kind of issue.


No it is a gas furnace.

It just periodically will not come on when it is to switch to the warmer temperature.

it has failed in the mornings when it is supposed to get the house to the warmer temperature and in the afternoon when it is supposed to get the house back up to the warmer temperature.

each time if i just turn the switch off and on a couple times on the furnace itself then it you hear the igniter start to suddenly click and then it takes off an runs fine.


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## Knotbored

Does it have a clock that is dependent on house electrical? Has there been an electrical outage and the thermostat clock not reset? 

I don't presently have a set-back type thermostat, but comments I hear about problems make me hesitate. They don't yet seem too efficient.


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## DevilRat

It could be that the electric ignitor is going bad. If the ignitor isn't on, the control valve won't open. There should also be a thermocouple on the ignitor, that if bad, also won't open the control valve. It could also be the solenoid on the control valve going bad. When they fail to trip, it won't open the valve to let the gas into the burners. 

*DISCLAIMER* I am by no means an expert on the matter. When in doubt, calll in a professional, especially when dealing with gas.


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## wacor

There is no issue with the power.

The thermostat has always read the correct time of day. Plus there is a battery back up.

I question if it is the igniter. The question is why it does this only when it has been in the cold cycle and it is going into the warmer cycle. 

I do wonder if when i turn off the power at the furnace and then turn it back on if it resets something in the thermostat


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## JohnWill

For a gas furnace, if the ignition doesn't take, there is usually a safety interlock that will prevent it from trying repeatedly. This prevents it from filling the house with gas and going BOOM!  I'd say it's either the ignition or the sensor going bad. I agree with DevilRat, for gas furnaces, I'd also call a professional.


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## wacor

I am familiar with the intent of a thermo coupler. If the unit does not ignite then it shuts things down so gas does not continue to pour out unignited.

does not seem like a thermo coupler issue though as I think when they go bad they are bad. Same would probably apply to an igniter.

Oh, well 

Only problem with calling somebody out now is that the problem is intermittent. I can see somebody just starting to replace parts trying to chase down the cause.


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## kilowatt1

I had a similar problem and it ended up being the thermostat. At first I had the same symptoms as you then I noticed that even when the thermostat seemed to function correctly, the room temperature was off by about 3 to 4 degrees. To confirm my suspicions about the programmable thermostat being defective, I purchase and installed a standard (non-programmable) t-stat. Problem solved. In fact, my natural gas bill was actually lower after installing the manual t-stat.


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## wacor

thanks for the input everybody.

that is weird killowat that your consumption would be lower. makes no sense. but whatever works best for you is good


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## lbt1

try jumping out the t-stat,that will tell you if its working ok


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## Space Cowboy

> Problem solved. In fact, my natural gas bill was actually lower after installing the manual t-stat.


Yeah .. same here .. having to heat up from a lower point then back will do this.

At least thats how my bud the furnace dude explains it ....


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## wacor

Space Cowboy said:


> Yeah .. same here .. having to heat up from a lower point then back will do this.
> 
> At least thats how my bud the furnace dude explains it ....


That seems to in some ways go against the logic. i wonder if it makes a difference how far you dial down at night i?


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## Byteman

Hi wacor, My home was flooded in June, so we had to replace lots of things, got a brand new hot air gas furnace among them. Airquest brand if it makes any difference, this one has the power vent, using a fan to pull exhaust combustion fumes to produce a positive draft in the chimney, this is the first one w/power vent I've had.
My symptoms were exactly what you are seeing> when the temp in the home dropped and the furnace should have kicked on, it did not, and I began also turning it on and off with the breaker as there is no switch on the furnace...it would always kick on when I turned the breaker back On. I called the installer, and when he got here, the darn thing was working correctly and has since....figures.
I will be trying some things, one mentioned was replacing first the breaker, then the stat, and get the company tech in for a test or two and I will let you know what we find out, or , maybe you will find out first...
The only change I made was to switch the blower fan speed to Medium/Low as they come with High speed turned on which was way to noisy and not needed here! That should not do anything but it does change the stack temp (higher) so, the furnace might not be starting if there is a sensor that checks temps and the thermostat cannot override the sensor....does that make any sense to anyone?
I left it alone the night before the installer guy came, that may have reset something he said....
Nights before that, i would get up every couple hours and manually turn it off, then on to get some heat.

This new furnace is a higher output BTU than we had, but we are seeing a lot less warmth!
Had a RUUD before that went 18 years with one problem, and that was caused by moisture and dust in the gasline. Plugged up the pilot valve. 
After the flood, water was in everyone's gas lines here, poured out of low pipes when they were opened.
No other gas appliances are malfunctioning so I dont think it's dirt or water in the gas lines,but we should check that out too.


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## wacor

Hi Byteman

Well for some odd reason the darn furnace has not acted up since my last post !!

The only thing I have done is to change the cooler temperature to raise it a few degrees. I had i set at 60 for the night and 68 during the warmer period. changed the 60 up to 65 since my kids were freezing at night.

in your case i would think you would know if it was a weak breaker as it should show it is tripped. i have seen breakers trip and where the indicator did not show. you could take the cover off the breaker box the next time your problem arises and then see if you have proper voltage coming out of the breaker.

the next thing i was going to try was as suggested bypass the thermostat. 

good luck to you. it is frustrating when something like this happens. i did not call a tech person yet because i figured they might not see anything if it was not failing when they were here and the problem is so intermittent


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## paisanol69

wacor said:


> Hi Byteman
> 
> Well for some odd reason the darn furnace has not acted up since my last post !!
> 
> The only thing I have done is to change the cooler temperature to raise it a few degrees. I had i set at 60 for the night and 68 during the warmer period. changed the 60 up to 65 since my kids were freezing at night.
> 
> in your case i would think you would know if it was a weak breaker as it should show it is tripped. i have seen breakers trip and where the indicator did not show. you could take the cover off the breaker box the next time your problem arises and then see if you have proper voltage coming out of the breaker.
> 
> the next thing i was going to try was as suggested bypass the thermostat.
> 
> good luck to you. it is frustrating when something like this happens. i did not call a tech person yet because i figured they might not see anything if it was not failing when they were here and the problem is so intermittent


I don't know if this will help you or not...programable setback thermostats work best in the summer months, when you are dealing with outside heat affecting your inside temperature. Depending on where you live, and how cold it gets, also what your house is made/built out of...

in the winter ( I speak from experience) if you live in a very cold climate, and you have long "turnarounds" in you heater on / off cycle to keep the house warm during activity times..

such as I live in Holland, and our house is made out of 5,000 psi poured concrete, with a brick outer layer, so when at night, I try to set the thermostat back to 60 deg f, the end result is, when I want it warmer in the day, it takes much longer to warm up the house, cause I set the overnight tem so low, the inner walls get cold, and take much longer to get back to a comfortable temp.

So...what I am trying to say is...it has been established, that is you want your house an average temp of 70 deg f, then at night, DONT turn the thermo down too low, thinking you are saving energy, cause druing the daytime/morning time when you want the house to be warm..the heating system works 3 times as hard to get it to the temp you want.

find a happy middle ground...ex:65 at night, with the prog on the thermostat, 72 in the morning from say 7 to 9...then back to 65 during the day, when nobodys home. This will prevent your heating system from cycling so many times...and in the end it will save you money on your energy costs, which is what we are all striving for. btw, even though I live in Holand, I have built 5 custom homes in the States, all in Texas.


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## wacor

that was another reason i had turned the low temp up to 65. i had heard the same thing although my initial thought was to lower it to 60 as the experts so to speak indicated there was a savings for every degree lower you set the temp.


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## valley

Wacor, my husband is an HVAC mechanic (heating/venting/air conditioning). If you havent resolved your problem as of yet, i'll ask him to take a look at this thread and see if there's anything he can suggest you to try before you hire someone to come in and look at it. 

I've got to ask you...what is the make, how old is it and when was the last time you had it serviced?


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## wacor

Thanks Valley

The furnace is original to the house. 1988

cant remember the make of it right now.

i have had only two service calls since i lived here which is 13 years old. 

The first one was due to the furnace not starting. as i recall there was just a cobweb which was blocking something to do with the igniter.

the other time the motor went bad. that was a couple years ago.

the odd part is that the furnace has run fine ever since i reduced the differential between the coldest and warmest temps. i did that about a month ago.

i am leaning towards it being an issue with the thermostat which is a White Rogers which is probably 5-7 years old i am guessing. 

Thanks again


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## valley

wacor said:


> i am leaning towards it being an issue with the thermostat which is a White Rogers which is probably 5-7 years old i am guessing.
> 
> Thanks again


I just showed the thread to Carl. He agrees thats its probably the thermostat. He says the expensive ones can be a royal pain. His advice, if you really want to know for sure if the problem the t-stat, is to throw out your 200 dollar White Rogers and switch over to a cheap Honeywell. If the problem is your thermostat then a new one would make the difference and will save you from the service call of a tech (minimum 40 bucks an hour, plus extra for parts if needed).

He also commented on the way you time different temps for different times of the day...no offense but he kinda chuckled at that and said something about it taking taking extra gas to fire up the furnace during all of those in-between times and you'd be better off keeping your thermostat set at one steady temp. (kilowatt mentioned that he actually saved fuel this way...carl says its true..you will save more fuel by keeping a steady temp instead of your furnace kicking on and off at certain times)

sorry we cant be more help. Someone else you might ask is Skivvywaver....he also does HVAC for a living.


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## valley

oh, and he says you really should have your furnace cleaned every year...if nothing else at least change the filter yourself and vacuum the dust out.


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## wacor

Thanks Valley

I should have mentioned that I do clean the furnace out myself as far as the filters at least twice a year

Gonna regroup on the changing temps. I have recently heard others say it is actually more expensive to do what i was doing. but i think it still is of benefit to dial it down a little at night from everything i have heard over the years


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## Frank4d

If it's not the thermostat then my guess would be the igniter. When the furnace tries to startup the igniter should glow very bright (white hot like a lightbulb). If it's just dim orange ot not at all, there's your problem. I replaced mine about two months ago for around $45.


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## Skivvywaver

Since Val mentioned my name.  Keep it at the same temperature IMO also.

I am not going to lean toward the ignitor if is is the glow plug type. They either work or they don't. There is not a thermocouple on new gas furnaces either. A thermocouple on applies to a standing pilot type of appliance. 

On new furnaces the t-couple has been replaced by a heat sensor. If the ignitor fires up and doesn't heat up to a certain point, the gas valve will not open. Usually after 3 attempts the board shuts down the furnace and flashes out an error code. 3 flashes from the LED would mean whatever is printed on the inside of the door.

So......You could have a bad ignitor. You could have a bad board. You could have a faulty heat sensor. Or you could have a bad thermostat and maybe even a bad gas valve.

It is very hard to say without being there with the proper tools to check it out.

I am leaning toward the thermostat myself. Those high dollar thermostats are known for malfunctioning. I have a digital but only for the fact that it is more accurate than and old mercury bulb type. I also have a new mercury bulb stat that I keep around for when, not if this digital gives up the ghost.


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## wacor

Thanks for the reply Skivvy

Not sure if you read the entire thread.

My concern in having a pro come check it out was that if it was working at the time it would be hard to diagnose. I work on water well pumps and the worst thing for us is to show up and find the pump working when we get there. Not always can we find out why it quit.

I am leaning towards the t-stat as the problem has not occurred again since i reprogrammed it. 

thanks


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## Skivvywaver

Yeah, I read it all and you are right. If it is working when I show up then IMO it isn't broken. 

I think it is the stat. That would be the first thing I would check. If you jump it out and it works, bad stat. Usually jumping the red wire to the white wire will bypass the stat. Check the wiring first though. Not everyone plays according to Hoyle.  It may never happen again. I hope that is the case Bill.


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## wacor

Thanks Skivvy


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## rhynes

Wacor, I was chasing ghosts out of the girlfriends furnace for a while, she had a similar problem... Her house is 60 years old, the furnace is 10 years old.

A tech came out from the gas company and told her she needed a new gas valve or something, $800 for the job but it wasn't a continual problem, very intermittant. Glad she didn't get it done.

Turns out the wiring to the furnace was spliced together in 4 places, no marettes or tape for that matter, and was mostly cat3 wiring, not enough. Installed a new Noma digital thermostat and new 18 guage solid core wiring to the furnace. 

Haven't had a problem since


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## Frank4d

rhynes said:


> A tech came out from the gas company and told her she needed a new gas valve or something, $800 for the job but it wasn't a continual problem, very intermittant. Glad she didn't get it done.


Heh.  Reminds me of a friend who called two contractors for estimates when his AC wouldn't run. One gave him an estimate for over $2000. The other flipped on the circuit breaker that had tripped (which fixed it) and didn't charge anything.


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## john1

Hi Wacor,

I read through the thread.
Yes, intermittent faults can be a problem to pin down.

If the problems start coming back, then here is my personal method
for helping to track and hopefully isolate intermittent faults.

I put small lamps on to various items that are involved with the
parts of the circuit that are playing up.
This will require an understanding of the circuits involved, and
how they interact.

I use small neon indicator lamps, they use such tiny amounts of
current that they will not put any additional load. (the current they
use is so low that they are sometimes put into screwdrivers as an
indicator which uses the persons skin as a current path.)
I use the type with the built in resistors.

For instance, if you suspect the electrical valve is part of the
problem, but you cannot tell if the feed is intermittent, or the
wiring to the valve, or the valve itself, then wiring a small neon
indicator(with int res) across the valve connections, and situating
this lamp in a place where it can be seen, then this will help you
to find a fault.
Next time the unit does not fire up, check if the lamp is lit.

If the lamp is lit, but the valve is not operating, then this tells
you something.
If the lamp is not lit, but the unit should have fired up, then this
tells you something else.

If the intermittent problem involves a few faulty or dodgy connections
then finding them can be very difficult, especially if those faults
don't show themselves after you get the covers off, and the meter out
to check here and there.

On occasion i have had various lamps temporarily wired to quite a few
places in faulty systems.
I have found this approach to be helpful because if the system does
not do what is expected, then looking at the lamps does not disturb
the system, and the information is relevant at the time of the problem.

It does usually require a circuit diagram in order to apply the info
to the system.

Best of luck with it,
John


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## wacor

thanks John

dog gone furnace has not acted up again. so waiting and wondering


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## JohnWill

wacor said:


> Gonna regroup on the changing temps. I have recently heard others say it is actually more expensive to do what i was doing. but i think it still is of benefit to dial it down a little at night from everything i have heard over the years


I can't imagine any reason that it's more efficient to run at full temperature all night vs. a setback. I'd be surprised if any credible source would say anything different.

The only exception is if you use a heat pump without the proper controls. My setback thermostats for my heat pumps anticipate when the temperature goes back up and start the heat pump in advance so the temperature is at the desired setting when the actual time is reached. If they don't do that, the electric backup (less efficient) comes on and negates some or all of the savings of setback.

Obviously, this is not an issue with oil or gas heat, since there is no differential in price, so I don't see any reason it wouldn't be more efficient.


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