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Old 11-05-2016, 11:36 AM   #1
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Pressure Switch/Condensate/Drain Issue - Gas Furnace


My gas furnace has worked fine since I purchased the home several years ago. This year, it starting having issues.

In short, it will cycle on, igniter glows, burners start, burners run for 10-15 seconds, burners flicker and then turn off. It will usually cycle a few times before going into lockdown. It gives a pressure switch error code (two blinks).

At first, I thought it was the flame sensor, I replaced and it has not changed.

Then it started giving me crazy blink codes, I looked at the control board and it was cracked and solder was melting. I replaced the control board and the problem has not changed.

I noticed the condensate tubes running from the drain pan to the pcv trap were blackened on the inside. I changed them out and the problem persists.

I've cleaned out the inducer fan hole. I've sucked on the pressure switch tubes and can here it click on blow and suck.

This morning, I disconnected the tube connected to the drain pan and it drained well over a gallon of water. The problem still persists.

I've attached some photos. Any ideas?








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Old 11-05-2016, 12:42 PM   #2
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Re: Pressure Switch/Condensate/Drain Issue - Gas Furnace


The drain trap may need to be removed and flushed with hot water and bleach if it has black scuzz inside. Should be flushed anyway.

Post the brand name and model # of furnace as it is not familiar to me.

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Old 11-05-2016, 01:00 PM   #3
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Re: Pressure Switch/Condensate/Drain Issue - Gas Furnace


Unit is Thermo Pride CHB1-100n.

When you say the drain trap, do you mean the black t and white pvc? I have taken those out and flushed them. Nothing major looks wrong with them. Water flows very freely.
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Old 11-05-2016, 02:02 PM   #4
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Re: Pressure Switch/Condensate/Drain Issue - Gas Furnace


On the lower right side of the exhaust fan the water flows out of the collector box and into a trap and then to the drain. That trap gets dirty and needs cleaning on some models. It may be in the fan compartment, hard to see where that hose goes.

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Old 11-05-2016, 02:05 PM   #5
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Re: Pressure Switch/Condensate/Drain Issue - Gas Furnace


Quote:
Originally Posted by yuri View Post
Post a pic of the right side of the furnace and where the water goes to the floor drain or condensate pump.
I might be missing something but, if you look at the photos I posted you should see this.

Water goes from collector box (port on right hand side of furnace), through a clear tube which runs to the left hand side of the furnace. You see this in the second and third photos.

This tube connects to a black T that is connected to a pvc trap that runs into the condensate pump.
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Old 11-05-2016, 02:09 PM   #6
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Re: Pressure Switch/Condensate/Drain Issue - Gas Furnace


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Old 11-05-2016, 02:18 PM   #7
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Re: Pressure Switch/Condensate/Drain Issue - Gas Furnace


Yeah, I looked again and edited my post.

However that clear tube must connect to a trap. The water has to drain into a trap or the furnace pressure switches won't close and exhaust fumes could leak out. Check inside the fan compartment. That is a rare brand and not one I see in Canada.
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Old 11-05-2016, 02:23 PM   #8
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Re: Pressure Switch/Condensate/Drain Issue - Gas Furnace


Here is a clear shot at where the tubing comes out of the furnace, into the black T and then into the PVC trap.

Also attached to the T is the drain from the bottom of the exhaust pvc pipe.

This is how it has been set up since I owned the home and have had no issues.

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Old 11-05-2016, 02:50 PM   #9
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Re: Pressure Switch/Condensate/Drain Issue - Gas Furnace


Did you physically remove the black tee and inspect it and clean it? If not it may be partly blocked inside. The pipe going from it to the pump may also be partly plugged.

After that you would need to get a differential pressure manometer and put it across the pressure switch to see what the vacuum is. You also need to know what the switch is rated for in "WC inches water column, which may be on the info tag on it.

If it is too low it may be tripping the switch and doing it's proper job. If it is good then the switch may be faulty. Check the intake and exhaust pipes very carefully outside for spiders webs, debris.

You may have enough air to fire the burner but once it gets going it trips if the amount is borderline. Some brands have a screen inside the intake pipe directly where it attaches to the furnace burner box. I have seen leaves get sucked in.
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Old 11-05-2016, 02:57 PM   #10
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Re: Pressure Switch/Condensate/Drain Issue - Gas Furnace


Took the T Off and cleaned it. Replaced the CPVC piping.

This made me realize, after some leaves got into the exhaust piping last year, I cleaned it out and this summer I added some mesh screen over the pipes to prevent anything more from getting in.

Is there any chance the mesh screen is restricting the airflow too much?
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Old 11-05-2016, 03:42 PM   #11
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Re: Pressure Switch/Condensate/Drain Issue - Gas Furnace


Yes.......

I have seen wasps nest inside those pipes and spiders webs etc so check it out. Also had a BKing wrapper get sucked in plus plastic garbage bags.

If you had leaves in the intake they may have got sucked further into the pipe. Carrier and one Lennox have a screen at the burner box on some older models.
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Old 11-05-2016, 04:18 PM   #12
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Re: Pressure Switch/Condensate/Drain Issue - Gas Furnace


Cleared the intake and exhaust. No issues noticed.

There does seem to be some condensate leaking from this seam. Not sure if this is an issue.

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Old 11-05-2016, 05:46 PM   #13
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Re: Pressure Switch/Condensate/Drain Issue - Gas Furnace


I don't know. Sometimes the gasket leaks behind the exhaust fan and water leaks down.

You may have to call a Pro to check the vacuum at the pressure switch or buy a manometer. Then you have to get adaptors for the hoses to the pressure switch which look large on yours and tee them into hoses to go to a manometer. Not as easy as it sounds.
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Old 11-05-2016, 07:05 PM   #14
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Re: Pressure Switch/Condensate/Drain Issue - Gas Furnace


Yuri, does that drain line set up need to be vented?
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Old 11-05-2016, 08:01 PM   #15
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Re: Pressure Switch/Condensate/Drain Issue - Gas Furnace


The clear hose is the trap. It doesn't run straight to the condensate pump. It bends up to the black tee, and then drains into the PVC pipe that runs to the condensate pump.

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