Forced air gas furnace pressure switches

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  #1  
Old 12-02-20, 07:26 PM
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Forced air gas furnace pressure switches

I'm hoping for some advice... or maybe clarification. My home is heated by a Carrier Comfort 92 furnace... Model 58MXB080-F-10112.

By no means do I consider myself an expert but I'm competent enough to replace standard parts. I decided heading into winter that I would get spares of some of the most common parts to fail... These things always seem to break on the coldest day of the year.

I want to order an igniter, flame sensor and pressure switch. The first two items seemed pretty reasonable at $35 and $38.... But the pressure switch seems to be coming in at over $150... I am in Canada, the land of expensive... I can import but the best USD price I can find is about $60... Which by the time I convert and pay for shipping comes in way over $100.

What's bugging me is that I see other similar switches for say, Goodman units starting at say $20.

The OEM numbers I have are:
Igniter: # LH33ZG001
Sensor: # LH680013
Pressure Switch: #
HK06NB124

Does anyone have any insight on why the prices on these are so varied? Or if perhaps they're interchangeable with a different, less expensive units with the same specs?

Also, are there any other parts you'd recommend on should have on standby?

Thanks
 
  #2  
Old 12-02-20, 09:18 PM
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I don’t know if I’d spend money on spare parts for that furnace. That model number is on the list of those affected by Carriers class action lawsuit.

http://hipspro.com/pubs/Furnace-clas...led_notice.pdf
 
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Old 12-02-20, 09:32 PM
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That is a U.S. Federal case. The OP is from Canada. Probably won't apply.

The flame sensor is nothing more than a stainless steel rod. I have never replaced one.
Just clean it with a green Scotchbrite pad. Make it nice and shiny.

The igniter is a must have spare part. The igniter can fail at the drop of a hat.

I have only ever replaced one pressure switch. They rarely go bad unless messed with.
I wouldn't keep a spare for myself.
 
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Old 12-02-20, 09:41 PM
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The unit appears to be in good shape. I've never heard of the class action case. Something I really need to look into.

@PJmax - Thanks for the advice. That'll save me some $. I was about to shell out for a pressure switch and sensor. I will get an ignitor to keep at the ready. Thanks!
 
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Old 12-03-20, 12:21 PM
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There were similar class actions in canada.
It's not the class action that makes the furnace problematic but the secondary heat exchanger design.
The secondaries have a plastic coating that comes off and plugs it up, resulting in extremely high carbon monoxide in the exhaust and eventually flame rollout. The heat exchanger also starts rusting from the inside out and leaking water.

Forget buying parts, beyond an igniter it's a waste of money.

Get the secondary visually inspected from the bottom and get a co exhaust combustion test done.

Things you can check yourself -> run it for 15 minutes and make sure the burner box closer to you is not getting hot. It's normal for the sides near the flames to get hot.
Sniff the exhaust for an off-smell.
Remove the trap and check it for plastic and rust flakes.

The trap should be cleaned every year on this style furnace.
 
  #6  
Old 12-03-20, 03:07 PM
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Now Iím getting nervous. It had been leaking. I thought it was the humidifier backing up. It wasnít.

I cleared out the drain again and a bunch of water and gunk that was clogging it came out. A friend (licensed tech) is going to come by to test the exhaust for carbon monoxide.

Iíll be mighty ticked if I have to replace a 14 year old furnace because of this exchanger.
 
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  #7  
Old 12-03-20, 03:39 PM
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Where is the water leaking? It could be something minor.

If it's at the back of the blower compartment, probably the heat exchanger.
The blower assembly can be pulled to see if it has rusted through - it's not a replacement for a combustion test. The combustion test would catch a plugging problem, but it can be rusted without being plugged and vice versa.


I’ll be mighty ticked if I have to replace a 14 year old furnace because of this exchanger.


You can get it replaced under warranty and class action covers some labor.

I think labor would be $700 to $1000 in the toronto area from most companies.
On another board I sometimes read, spotted this...
*I would link you but mods would probably delete it.
$500 is very good for heat exchanger replacement. I don't know the company.

Originally Posted by post from other forum
Hello

just had my 12-year Carrier secondary heat exchanger replaced for $500 labor...part was covered by Carrier 20 yr warranty.
Got quote for a new replacement for $4,000 + taxes.
Carrier trade-in would have given me $800 allowance plus
Enbridge Gas gave me another $750 if I had an audit done which would cost me $150 so net would be $600 (see link removed by me)
so a new carrier furnace would have cost me $4000+452 (taxes)=$4,452-800-600=$3,052

I opted for the $500 labor ….job was done by an excellent Certified Carrier Dealer who sent a very friendly and knowledgeable technician
I also have a monthly parts+labor service plan with the dealer

Here is the company that replaced my Heat Exchanger
https://hargraveheating.com/

Thanks


 
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Last edited by user 10; 12-03-20 at 05:55 PM.
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Old 12-03-20, 04:32 PM
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Good information. You are correct about leaving service websites up but I consider this fairly important and as it's Canada the links will stay temporarily.
 
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Old 12-03-20, 04:40 PM
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These furnaces affected Canada as well, they were widely distributed.
Early on in the failure, a combustion test will show readings slightly off from normal. As the failure progresses (there’s no way of preventing or stopping it) the combustion numbers continuously degrade to the point where the occupants can smell an odor outside near the exhaust termination. In some cases exhaust CO (carbon monoxide) becomes so high it can begin leaking back into the house and causing a potentially dangerous CO situation.
Pretty much all of these furnaces on the list will suffer secondary failure at some point.
 
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Old 12-03-20, 05:53 PM
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Something eventually takes out all furnaces - if this style model lasts 20 years without the secondary failing, it's a success.
 
  #11  
Old 12-03-20, 07:40 PM
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The water was leaking out the bottom of the unit. definitely not coming from the humidifier. I blew into the drain that leads up past the blower into the heat exchanger area. Loads of water and gunk came out. mostly black.... maybe some rust.

I appreciate the links and will investigate. I'm not sure where to start. If I should contact Carrier? Or one of their authorized dealers? My friend is a licensed HVAC tech but he's a one man show and isn't affiliated that way. I talked to him again earlier and he said that if it is covered by warranty it wouldn't be him... and he thinks it'd cost $1500.
 
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Old 12-03-20, 07:58 PM
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Do as I suggested - run the furnace for 15 minutes, feel the burner box (not the sides closest to the flames), smell the exhaust. Normally the exhaust has no smell.

Was the water leaking out just around the trap area or further back? Water at bottom near the front is less concerning.

It's worth having your friend or someone else check the combustion and gas pressure, particularly it's done with a full analyzer and not just monoxide. Maybe even pull the blower assembly.

The full analyzer measures oxygen and temperature and can give a better indication, as other things can cause high monoxide.

If the heat exchanger has failed and you want to repair it under warranty, start calling around - carrier dealers are naturally preferable.

I would not put close to $1500 into that furnace as other expensive repairs may come like the inducer and circuit board. It's also a basic single stage one and aging - 2-stage is much better for comfort and you would get a 10 year parts warranty.

It could also be oversized for house and ducts. 80 000 btu furnace is large -> have no wall insulation or a big house to justify it.

$800 and lower could be worth it but it's your call.
It's worth contacting that company I linked to just in case - I personally have zero experience with them but they have good reviews and someone got it done for $500.

Here's another: https://www.furnaceacexperts.ca/carr...r-replacement/
*Mod will probably remove it soon.
 
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Old 12-03-20, 08:09 PM
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@user 10

Would you know approximately how long ago that $500 warranty replacement was done?
 
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Old 12-03-20, 08:15 PM
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The sides feel hot but I don't know how hot is too hot. There are no add smells. Just as a precaution I put a second carbon monoxide alarm in the room.

Water was leaking from underneath at the back of the furnace.

He said he's bringing multiple analyzers. So I imagine he's covering that.

I just put a message in to Hargrave.

Thank you!
 
  #15  
Old 12-03-20, 08:18 PM
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I'll PM you more info.

Edit:

The side of the burner box right under the rollout switch should not be hot! You should be able to comfortably keep your fingers there - cold to luke warm is normal. The rollout has two wires and a little button.

With water leaking from the back of the furnace - even if it passes the combustion test, the blower really needs to be pulled and secondary checked for rusting. It's most likely rusted through!

It can be rusted but not plugged.

Keep us updated.
 

Last edited by user 10; 12-03-20 at 09:19 PM.
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Old 12-03-20, 08:46 PM
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Not to be a downer but from what you describe, it’s showing the classic symptoms and of a failing secondary.
The combustion test will be the true judge.
Are your CO detectors UL listed (I don’t even know if there is such a thing in Canada)? If so they are purposely set to not go off until CO rises above 70 PPM for a minimum of 4 continuous hours. So your house could have 69 PPM of carbon monoxide 365 days a year and it would never go off.
Basically they are for an all out major failure. Like a rotted breech or clogged chimney.
Low level CO detectors are what you want.
 
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Old 12-03-20, 09:20 PM
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Canadian co alarms have to meet the same standards. 70ppm trip point, between that and 30 ppm it can't alarm for 30 days. Below 30ppm, no alarming what so ever!

We have ULc.

The ones with digital displays are better, they indicate before levels hit the alarm threshold.
 
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Old 12-03-20, 09:30 PM
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This is 3 meters from the furnace. I bought this today. I didn't think zero was possible.


 
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Old 12-03-20, 09:39 PM
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I think you have to hit peak level to read below 30ppm - but this may have changed and 30 is still the lower limit.

By the time you have monoxide in the house at 30+ ppm, you may have thousands in the exhaust as these secondaries don't leak directly into the house air. It's more like idling a car with a cold engine close to the house and it can leak in, but closest analogy i have.

Still good to have the alarm with the display.
 
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Old 12-03-20, 09:49 PM
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I started this whole thing with the desire to be prepared for winter with a few parts.... and now it's looking like my 14 year old furnace has major issues.

I appreciate the insight here.... Safety is foremost... I'm handy but this is not my trade. The help here has pointed me in the right direction and potentially saving me a bundle.

Thank you.... This seems to be a common problem. Others may benefit so I'll report back as I learn what's happening.
 
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Old 12-03-20, 09:53 PM
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Don’t feel too bad. Some DIYers throw hundreds of dollars of parts at their furnace issues, only to be told they have one of these and there’s not much to be done. Even with lawsuits and such a lot of owners haven’t a clue they have a furnace with factory problems.
 
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  #22  
Old 12-06-20, 09:22 AM
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My friend came by and ran the tests. Exhaust CO is 6 PPM.... He suggested the leak is internal and recommended that if I can get the warranty done at a decent price it's worth it.

In the utility room the CO detectors are still showing nothing....

One way or another I ca't have a rusting out exchanger in there. I didn't hear back from the one Carrier authorized outfit. I will have to make some calls tomorrow when they're open.
 
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Old 12-06-20, 10:10 AM
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What were the other combustion test numbers? Often a failing secondary will have all the numbers screwed up.
 
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Old 12-06-20, 11:13 AM
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Need to identify the source of the leakage before going further.
There is specific criteria to identify failure.

Possible the furnace is sloping back a bit and it's actually coming from the front.

The blower assembly needs to be pulled for a visual inspection. It's a pain on this furnace but needs to be done.
It's possible to have a spot where the coating has failed and it's rusted though without having it plugged up.

 
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Old 12-06-20, 05:17 PM
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He did a combustion test. Going my memory now. He mentioned something about 9% I think referring to O2 levels... I hope I picked up on that correctly because he went quickly into saying that the fact that the secondary is accumulating rust and debris from the inside and fouling up the works just means that it's on it's way out.... even if the readings were borderline acceptable at the moment. He said I would need to decide "when" I want to deal with it, not "if" I want to deal with it.... to that effect. It was this morning (Sunday) at 6 am so I was little fuzzy..... LoL! It was the only time he was available on short notice. I was red-eyed but grateful.

At this point re recommended first to find out if a warranty repair could be done for a price reasonable enough to be worth it... He said I need to make the decision but offered up similar advice to you guys. That being it's not worth Over $1000 to repair. I've known him for over 30 years. He's a good guy wasn't trying to pressure me into a new furnace. He just said if I'm interested in going that way to let him know.

I have calls to make... I hope I can reach Hargrave.
 
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Old 12-06-20, 07:31 PM
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You can't really tell what's happening on the inside of the secondary other than it's not plugging up yet.
9% oxygen is normal, if not a little high.

The material may start degrading and it's not enough to plug it up. I'm bringing this up because you said there was water leaking.
You can not get the secondary warrantied if it's not bad yet. Carrier wants at least 200ppm of co in the exhaust or visual signs/rusting.

It must be verified.

If there are no signs of failing beyond a little rust in the trap, continue to run the furnace as is.
With the blower out, if any part of the secondary rusted through - yes, get it fixed.

---------
Actual criteria:

200ppm with every other cause ruled out and or
"Perforation due to corrosion* Fatigue cracking Split heat exchanger seams If any of these items are identified, replace the appropriate component. If no external defects are found, remove the coupling box cover at the rear of the furnace. The cold spot baffle is undernea"

*A water leaking secondary would qualify.

Source:https://siglercarrier.com/wp-content...dsb09-0022.pdf
 
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Old 12-06-20, 07:51 PM
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Makes sense. I wonder.... if I call the Carrier authorized repair people... I assume I'm in for a steep bill if they pull the blower out to verify...... and if it's not rusted through....... Only to find myself with an exchanger which isn't bad enough for warranty replacement.... but dying a slow death nonetheless.....

 
  #28  
Old 12-06-20, 10:14 PM
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You would have to pay the labor - could be an hour plus a service call.
It is important to identify the source of water leakage.
Did you notice the water during the heating season? Is the humidifier mounted on the supply by any chance?

Pulling the blower is semi-diy friendly -> power off, the condensate trap has to be removed and the part the board is mounted to, unscrewed and pushed out of the way. The blower and potentially thermostat wire gets disconnected (blower speeds get noted), after that it's two screws.

With the blower out you crawl into the furnace head first and carefully inspect the secondary.

Good opportunity to wash the blower assembly if it has dust buildup.

This is best done on a milder day in case you screw up.
 
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Old 12-06-20, 10:38 PM
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Agreed. Worth paying to pull the blower for a more extensive inspection.

There was no water until heating season... however not coming from the Generalaire humidifier.... It's definitely coming from the area of the secondary exchanger. Whatever the drain comes from.

From the look of the AC coil I imagine there will be a lot to clean up in there. I get the sense that... if possible... thorough cleaning on a regular basis would ensure a well built furnace lasts a very, VERY long time.
 
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Old 12-06-20, 11:30 PM
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entire secondary drains into collector box, then out into the trap.

If you can see the underside of the evap coil, you should be able to see the heat exchangers and may be able to inspect a little from above.

Otherwise, maybe call these guys into the week and just say water leaking into blower compartment. if they don't pull the blower for inspection, request.
 
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Old 12-07-20, 11:25 AM
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I called Hargrove this morning. They were at my house by 12:30. He pulled the blower and did a full inspection with readings. I was expecting to need to decide between an exchanger or a furnace.

He said my exchanger is just fine. He said the drain and trap had been clogged. The water built up and it had nowhere to go but up and out.





 
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Old 12-07-20, 12:29 PM
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I called Hargrove this morning. They were at my house by 12:30. He pulled the blower and did a full inspection with readings. I was expecting to need to decide between an exchanger or a furnace.


Thanks for the update.
It's good to have a pro go over the entire unit every couple of years at this age.
The trap should be cleaned every year and that's diy friendly.

Did you like the contractor?

Did he do anything else like check gas pressures, etc.
The furnace actually looks quite under-fired -> not just high oxygen but low stack temperature, granted the low stack temp could be from checking it before the furnace had a chance to reach steady state.


If you want, PM me what they charged, as I may refer them based on feedback. Good contractors who actually want to repair/service and not sell new are few and far between.
 
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Old 12-07-20, 04:07 PM
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PM sent.

I really liked this contractor. Very professional and polite.

Iím not sure what you mean by ďunder firedĒ?
 
  #34  
Old 12-07-20, 04:19 PM
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Underfired just means it's burning less fuel than it should - which changes the fuel to air mix and reduces the exhaust temperature, hence highish oxygen and lower temp.
BTU input below the 80 000 btu rating.
Most likely cause is gas valve pressure set a little low.
Not a big deal when the furnace is larger than required, slightly cuts efficiency.

The temperature reading may not reflect what it stabilizes at so I won't jump to the conclusion it's under-fired.

Leave it alone for now, next time you have a tech if you want ask if the gas pressure can be checked, assuming it wasn't done this time.

It's safe and that's what matters.



 
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Old 12-07-20, 04:23 PM
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Understood. Thank you! Indeed safety is the the most important factor by far.

And back to my original reason for starting this thread...... I picked up a spare igniter this afternoon ... LoL!
 
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Old 12-08-20, 07:56 AM
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Just keep in mind, you have one of the marked furnaces. Probably a good idea to get it tested every year. Not really a question of if, but when it fails.
It’s usually a slow progression so it’s nothing that you’ll come home to one day and it’s all of a sudden failed.
 
 

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