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Old 12-06-2011, 01:13 AM   #1
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Furnace not lighting consistently


Hi all,

new homeowner and complete newbie when it comes to furnaces. My furnace (20 year old mid efficiency with a honeywell circuitboard) is failing to light and then all of a sudden will start working after some time. The blower fan stays on, pumping cool air. I checked the status lights and it says that the pattern means 2 things:

"Retry Delay - third failure to light on same call for heat. New trial for ignition after five minute delay." (makes sense, I hear a loud noise every five minutes when it is acting like this).

"Marginal flame signal - system may not operate reliably over time."

I am wondering if anyone here knows about these issues generally, whether they are generally a big deal or whether the can be dealt with easily through calling a service technician. The costs with this house are piling up...

Thanks all.

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Old 12-06-2011, 01:25 AM   #2
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Furnace not lighting consistently


Posting the brand and model of the furnace will result in less guessing from this end.

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Old 12-06-2011, 01:29 AM   #3
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Furnace not lighting consistently


Duomatic Olsen HMS2-105H
Honeywell S8610U
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Old 12-06-2011, 10:16 AM   #4
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Furnace not lighting consistently


The most common fault that will cause your problem will be a dirty flame sensor which is a thin rod held in a porcelon base that sits in the furnace flame path. The first thing to try would be to clean the metal part of that flame sensor with a wire brush or steel wool.
Do this with the power off to the furnace. If this is beyond your comfort range then maybe you should ask your neighbours who they are happy with who services & repairs their furnaces
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Old 12-06-2011, 01:00 PM   #5
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Furnace not lighting consistently


See video for how's recommendation.

Check batteries (if any) in thermostat).

Check for obstruction in discharge to outdoors.

Check for condensate drainage problem (clog) if applicable. Not sure your model.

http://www.youtube.com/watch?v=I86joWL66aE
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Old 12-06-2011, 02:15 PM   #6
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Furnace not lighting consistently


I found my flame sensor/ignition piece but it is way at the back and I can't even get the screws out for it...

It's the white nubbin, the red cable is usually attached.
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Old 12-06-2011, 03:03 PM   #7
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Furnace not lighting consistently


it is a combo flame sensor and igniter. need to CAREFULLY remove it and clean the rod on the porcelain. that furnace is obsolete and the co. that made it went broke. name is around now as it got sold to someone else but it is not the same furnace etc. I would not spend a lot of $$ on it as it has old parts which will nickel and dime U to death and develop intermittent nickel and dime U to death problems.
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Old 12-06-2011, 03:12 PM   #8
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Furnace not lighting consistently


shut the gas cock off into the furnace not the valve but up on the pipe...loosen the silver aluminum tube off the valve that's your pilot gas feed(break it with an ajustable then loosen with your fingers...see that screw under the pilot tube in the pix 5/16ths need to unscrew that and pull the aluminum tube with the assembly out...that orange wire needs to go back in that white fitting it is your ignition wire.... for spark.if you don't have a bear wire about 1/4 showing strip it so it makes contact...
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Old 12-06-2011, 07:25 PM   #9
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Furnace not lighting consistently


A dirty pilot orifice is the other most common cause of a pilot failure on this system. A restrictive pilot orifice can make the ignition or its verification an intermitant problem like you've reported.
The solution involves removing and dissembling the pilot assy for cleaning or orifice replacement.
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Old 12-06-2011, 07:36 PM   #10
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Furnace not lighting consistently


On an old consolidated without a contro board today the pressure switch was not closing or when it did it would hold only for a few seconds at a time, causing the spark ignition to either not ignite or ignite and then cut off.

Only way the furnace would stay lit was by way of me and I wasn't spending the night in anyone's attic sucking on a tube so they can stay warm.

It was after hours.

Just thought I mention that as there was no codes (no board) but that was the problem.
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Old 12-06-2011, 07:44 PM   #11
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Furnace not lighting consistently


Thanks for the tips guys. The problem I have noticed seems to be getting worse or I am just noticing it more. The furnace fan will come on for over an hour before the flames will successfully light. When it gets to -20C I might be in trouble (Edmonton). There are rebates up here for new furnaces but I already have a lot of other expenses.

No reason to think that if I fix this for $80 the furnace shouldn't continue working for many more years, right?
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Old 12-06-2011, 07:53 PM   #12
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Furnace not lighting consistently


Nope. Most service companies will charge you $3-400 to change that pilot assembly. You may have a problem with that S86 control and that is $600 and up. I have worked on hundreds of those units and most of them have been replaced due to cracked heat exchangers or cost of repairs or problems getting parts.
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Old 12-06-2011, 07:55 PM   #13
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Furnace not lighting consistently


If you are willing to fix it yourself then all you will know is that the furnace is producing consistant heat. The safety aspects of a heat exchanger inspection are better left to a HVAC guy that your neighbours are already using and are pleased with.
I had three different calls today from folks complaining that the HVAC that just left their house was only interested in scaring them into a new furnace.
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Old 12-06-2011, 07:59 PM   #14
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Furnace not lighting consistently


Ugh. Perhaps the situation is worse than I thought. I was just looking at my energy company's $80 furnace maintenance deal. Assuming they would clean and fix everything simple and hope that would resolve the issue.

I just observed it while it was trying to light. The spark caused a small flame in the nearest burner, which went on for a second and then just cut out. Don't know if that helps to narrow the possibilities at all...
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Old 12-06-2011, 08:07 PM   #15
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Furnace not lighting consistently


the spark needs to sound loud and light the pilot flame which should be about 1-2" long and strong. then it allows the gas valve to open and light all the burners. sounds to me like a bad pilot burner and that S86 control is failing. gas valve could be shorting internally etc etc. you need to find an old school tech who knows the older equipment. new school guys are familiar with the modern circuit boards and flame sensors but that furnace is like a car with a carburetor. most mechanics don't know them either.

financing 101: buy a $4800 furnace divide by 5 yr payment plan/60 months. payments are $80/month or spend $600 or more to repair it which could give you 8 or more months of furnace payments. have to spend some serious $$ either way. there is some rebate $$ from the ecoenergy fed program and a high efficiency furnace may save you about $200 at least in fuel which buys you a couple more monthly payments.

it is repairable but not a good value for your $$ IMO. in Wpg. we can finance furnaces thru the gas co and their rate is less than 5%. check with yours.

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Last edited by yuri; 12-06-2011 at 08:21 PM.
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