#1  
Old 04-30-2016, 09:21 AM
Trevor89 Trevor89 is offline
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Furnace question

Hello all, I have been having an ongoing issue with my furnace. It is a regular 80% efficiency that is more than 15 years old now, around there anyway.

What's been happening is every once in a while, the thermostat calls for heat, the exhaust fan fires up but nothing else does. It will run like this until I go and take the blower panel off and put it on again which usually causes it to fire up normally.

This morning I woke up to it doing it again, this time I took the panel off and put it back on and I watched through the burner viewing port that the hot surface igniter glowed for a few seconds and then shut off. I took the panel on and off again and this time the igniter glowed and the burners fired up within a couple seconds and all is well again.

I'm perplexed as to what it could be since it is an intermittent issue that is usually fixed just by 'resetting' the cycle so to speak. As far as I know it's been the same thing everytime, the process works up until it's time to fire the burner and then it stops until the next time you try or maybe the time after that and then it's good to go for a while. I thought when most things failed on a furnace they just failed and that was that, no back and forth.

Any and all advice is appreciated before I bite the bullet and call a tech in.

Thank you.
  #2  
Old 04-30-2016, 09:39 AM
beowulff beowulff is offline
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Sounds like a defective interlock switch.
  #3  
Old 04-30-2016, 09:44 AM
Trevor89 Trevor89 is offline
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I think I may have tried switching it off and on at the breaker one of the first times it happened and it worked after that, but I can't remember for sure. Next time it happens I'll have to try that and see if it works. It may be worth just replacing the door switch to see however it shouldn't be too pricey or complicated to at least give it a shot. Thanks for the insight.

Is there anything else it could be? Other than I guess a fault control board but I hope that isn't the case.

Last edited by Trevor89; 04-30-2016 at 09:45 AM. Reason: Sounded stupid.
  #4  
Old 04-30-2016, 09:51 AM
Joey P Joey P is offline
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My suggestion would be to pull the bottom panel off and see if you see the little blinking light (you may have to pull off the cover to access the circuit board if there isn't a window). There should be a legend to tell you what it means.
If it says it's 'okay', then fire it up so it fails and read it.

After the igniter started glowing, did you see any flames at all? Even just for a second? If you did, it's probably a bad or dirty flame sensor. You can clean them, but they're easy to replace.

But check for a code, it should tell you where to start.
  #5  
Old 04-30-2016, 09:54 AM
Trevor89 Trevor89 is offline
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I can say for sure there was not a hint of flame when the glow igniter fired up the first time I saw it, but it also seemed like it didn't stay on as long as it should before it shut off. That's just a gut feeling though I have nothing to base it off of.

I will try looking for the blinking light when I get home from work. Hopefully it's new enough to have one, I don't remember seeing one before..
  #6  
Old 04-30-2016, 10:06 AM
Joey P Joey P is offline
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I would guess it would, but I could be wrong. Usually if you pull off the bottom panel, you'll find another box. Often times that box has a small window that you can view a blinking light. If not open it (keeping in mind there's 120v and low voltage in there).

Another thing that it could be is a bad gas valve (or, I'm reading, high gas pressure). You can test that, I saw mention of just running the low voltage wires right to the valve to see if it clicks...make sense. But I think I would first start by hooking my meter up to the gas valve leads and seeing if it's calling for gas or even just listening and/or smelling to see if I think it's calling for gas.
In fact, that's probably the next thing I'd do, put my multimeter across the valve leads and see if it asks for gas when it doesn't fire. If it does, my money would be on a bad valve. And, in this case, the blinking light would say that no flame was sensed.
  #7  
Old 04-30-2016, 10:14 AM
Trevor89 Trevor89 is offline
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That's good advice I will try that the next time it doesn't fire up. My only problem may be is when I put the multimeter on it it will probably all work fine that time like it always seems to do on the second or third attempt haha. I couldn't get lucky with a straight forward failure.

I did notice that after the exhaust fan would start back up I would hear a distinctive 'click' from the gas valve control box or module and the glow igniter lit up and shut off. Then the second attempt I made there was the same audible 'click' only this time the igniter stayed glowing for a second or two longer and the burner went up like a charm.

The click seemed too loud to just be the igniter firing up I assumed it would be the gas valve opening but perhaps not. With the exhaust fan running I wasn't able to hear any gas flow and I couldn't smell any either but I don't think I've ever heard or smelt any gas with this furnace.
  #8  
Old 04-30-2016, 10:25 AM
Simmerdown Simmerdown is offline
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Furnace question

This happened to me this winter. Turns out it was the flame sensors. Kind of like a thermocouple on a water heater. I pulled them out and cleaned them off with some steel wool. Popped them back in and haven't had a problem since.

(I see Joey P already covered this)

Last edited by Simmerdown; 04-30-2016 at 10:28 AM.
  #9  
Old 04-30-2016, 10:29 AM
Trevor89 Trevor89 is offline
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I greatly appreciate yours and all the advice thus far. I'll attempt to clean the flame sensors tonight and then wait and see if I have any further issues.

Next time I'm in the States I'll buy y'all a beer, American or Canadian your choice
  #10  
Old 04-30-2016, 10:45 AM
Joey P Joey P is offline
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Quote:
Originally Posted by Simmerdown View Post
This happened to me this winter. Turns out it was the flame sensors. Kind of like a thermocouple on a water heater. I pulled them out and cleaned them off with some steel wool. Popped them back in and haven't had a problem since.

(I see Joey P already covered this)
Quote:
Originally Posted by Trevor89 View Post
I greatly appreciate yours and all the advice thus far. I'll attempt to clean the flame sensors tonight and then wait and see if I have any further issues.

Next time I'm in the States I'll buy y'all a beer, American or Canadian your choice
A dirty flame sensor will only be the problem if you saw a flame before the entire unit shut down.

Now, it's possible that your furnace checks to see if the flame sensor is working before firing up (never heard of that, but each model is different), and yours is on the fritz. But in that case, you'd still have a code for it.

My guess is whatever it does between lighting the hot surface and checking for a flame. That, I'm thinking, is pointing towards the board or the gas valve. But I'm seeing posts on the internet of gas orifices that need to be cleaned and causing similar problems.
  #11  
Old 04-30-2016, 10:51 AM
Trevor89 Trevor89 is offline
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So to clean it I assume you would remove the gas valve itself and check the lines and/or ports? Or is there some quick easy way I'm unaware of?
I will try cleaning the flame sensors too just in case but yeah it shut off before the flame arrived.
  #12  
Old 04-30-2016, 11:01 AM
Joey P Joey P is offline
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Quote:
Originally Posted by Trevor89 View Post
So to clean it I assume you would remove the gas valve itself and check the lines and/or ports? Or is there some quick easy way I'm unaware of?
I will try cleaning the flame sensors too just in case but yeah it shut off before the flame arrived.
To clean the gas orifice(s)? I'm not sure, I'd poke around on the internet. I don't think it involves removing the entire valve or even touching anything 'pressurized' (for lack of a better word). Just one small pipe or (even just the brass fitting at the pilot end) and blowing it out with compressed air.
  #13  
Old 04-30-2016, 11:12 AM
Trevor89 Trevor89 is offline
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Ok I'll muck around with trying to clean the orifices and the flame sensor for the hell of it and see if that changes things. If I find anything out or have to get a tech I'll inform on here what the issue was to try and help someone else with problems.
  #14  
Old 04-30-2016, 12:15 PM
K364 K364 is offline
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Same problem three times

Always the Flame Sensor
  #15  
Old 04-30-2016, 12:25 PM
Trevor89 Trevor89 is offline
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Did you resolve this by just cleaning the flame sensor each time or by replacing it?
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