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Furnace not always starting


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wacor's Avatar
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14-Nov-2006, 07:44 AM #1
Furnace not always starting
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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14-Nov-2006, 09:22 AM #2
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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14-Nov-2006, 09:30 AM #3
Quote:
Originally Posted by 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.
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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14-Nov-2006, 10:25 AM #4
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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14-Nov-2006, 11:19 AM #5
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.

Last edited by DevilRat; 14-Nov-2006 at 11:26 AM..
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14-Nov-2006, 01:38 PM #6
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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14-Nov-2006, 02:17 PM #7
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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14-Nov-2006, 02:22 PM #8
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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14-Nov-2006, 06:17 PM #9
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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14-Nov-2006, 09:28 PM #10
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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19-Nov-2006, 11:54 AM #11
try jumping out the t-stat,that will tell you if its working ok
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19-Nov-2006, 06:58 PM #12
Quote:
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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19-Nov-2006, 07:01 PM #13
Quote:
Originally Posted by Space Cowboy
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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09-Dec-2006, 01:43 AM #14
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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Last edited by Byteman; 09-Dec-2006 at 01:50 AM..
wacor's Avatar
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09-Dec-2006, 10:02 AM #15
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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