# Pressure Switch/Condensate/Drain Issue - Gas Furnace



## JerLon (Oct 23, 2014)

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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## yuri (Nov 29, 2008)

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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## JerLon (Oct 23, 2014)

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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## yuri (Nov 29, 2008)

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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## JerLon (Oct 23, 2014)

yuri said:


> 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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## JerLon (Oct 23, 2014)




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## yuri (Nov 29, 2008)

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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## JerLon (Oct 23, 2014)

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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## yuri (Nov 29, 2008)

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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## JerLon (Oct 23, 2014)

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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## yuri (Nov 29, 2008)

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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## JerLon (Oct 23, 2014)

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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## yuri (Nov 29, 2008)

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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## ZTMAN (Feb 19, 2015)

Yuri, does that drain line set up need to be vented?


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## beenthere (Oct 11, 2008)

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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## yuri (Nov 29, 2008)

ZTMAN said:


> Yuri, does that drain line set up need to be vented?


No. The newer furnaces in some brands like Lennox do but some of the older ones don't. I have had to vent a few Ducanes that would not drain fast enough but that was because of the long horizontal drain hose running thru the fan compartment not having enough slope.


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## yuri (Nov 29, 2008)

There are many different ways to make a trap. That is a rare furnace not seen in my area but a trap is a trap. Goodman has that simple bucket open type sticking out the side and you can see open water in it and it is bulletproof simple. Cannot use it on horizontals which I am not sure they have. Lennox is mostly all multi-position with one type of trap.


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## supers05 (May 23, 2015)

For drain venting it's always best to read the manual.  

Cheers!


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## supers05 (May 23, 2015)

How old is this furnace? Probably need put a manometer on across the heat exchanger. (I'm thinking the secondary is starting to plug up) Do you only have 1 Vent pipe, or also a combustion air pipe? (2 pipe system) 

If you have an amp probe, take a current reading of the inducer motor when it's up to speed and the furnace has lit. (I understand that you won't have much time) Report the reading with the name plate RLA for the motor. 

Cheers!


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## yuri (Nov 29, 2008)

Looks like a 1 piper.


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## beenthere (Oct 11, 2008)

Its 2 pipe. The front pipe is the combustion air, below and behind that is the inducer and its exhaust pipe.


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## JerLon (Oct 23, 2014)

beenthere said:


> Its 2 pipe. The front pipe is the combustion air, below and behind that is the inducer and its exhaust pipe.


This is correct.

I'm thinking that I may be past the point of DIY on this one given no one sees an obvious solution.


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## supers05 (May 23, 2015)

JerLon said:


> This is correct.
> 
> I'm thinking that I may be past the point of DIY on this one given no one sees an obvious solution.


I saw the 2 pipes inside the furnace, just checking if they both actually run all the way outside.

At 7 years the it's up there in age. Since it's clearly older then that, it's getting old. Single pipe systems, or duals in areas with lots of dust will have a fairly clogged secondary heat exchanger by now. It'll be like concrete though, so it isn't easy to fix. That's why you need the the manometer. If you don't have one, it's time to call a pro. That's a no name brand, so don't count much on any kind of warranty, and the likely chance that you'll be replacing it. 

Cheers!


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## JerLon (Oct 23, 2014)

Had a pro come out today from a reputable local company. He is convinced that it is the control board. 

My only reservation is that I replaced the control board. Same symptoms before and after replacing the control board.

He thinks it is the control board because it is giving an error code that makes no sense given the symptoms and nothing else appears wrong. That is the same line of logic that caused me to replace the control board. 

Any thoughts on the odds he is right/wrong?


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## beenthere (Oct 11, 2008)

Refresh my memory. Did you clean out all the drain hoses. Did you remove the burner box cover and run it to see if it stays burning then?


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## JerLon (Oct 23, 2014)

beenthere said:


> Refresh my memory. Did you clean out all the drain hoses. Did you remove the burner box cover and run it to see if it stays burning then?


No, never removed the burner box cover. Is this safe to do? What might this be indicatave of? 

Yes, replaced all drain hoses.


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## beenthere (Oct 11, 2008)

Its safe. 

It will indicate if there is a problem in the combustion air intake. If it burns longer, then sputters out, and gives pressure switch error. Points toward an exhaust pipe problem.


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## JerLon (Oct 23, 2014)

Interesting results. Doesn't run any longer with burner box open. 

However, I've noticed that this problem seems to be occurring more when I open the service door (top door with access to inducer, pipes, burner...). Last night it was working fine and I went to look at it and the problem occurred as soon as I took the door off. 

Reset furnace and left the door on and the furnace worked all night. 

The lower door on this furnace has the safety switch so that has nothing to do with it. 



beenthere said:


> Its safe.
> 
> It will indicate if there is a problem in the combustion air intake. If it burns longer, then sputters out, and gives pressure switch error. Points toward an exhaust pipe problem.


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## supers05 (May 23, 2015)

JerLon said:


> Had a* pro* come out today from a reputable local company. He is convinced that it is the control board.
> ...
> Any thoughts on the odds he is right/wrong?





JerLon said:


> Interesting results. Doesn't run any longer with burner box open.
> ..


Did he actually take any of the measurements that we've asked for? Pressure at the switch? Across the heat exchanger? After after the inducer if possible? *Manifold pressures?*

Cheers!


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## JerLon (Oct 23, 2014)

supers05 said:


> Did he actually take any of the measurements that we've asked for? Pressure at the switch? Across the heat exchanger? After after the inducer if possible? *Manifold pressures?*
> 
> Cheers!


He says he did all of these items and none were concerning.

The furnace has been running fine for a week. I took off the cover today and it stopped again after about 15 seconds.


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