# Perplexing problem, Ruud furnace



## jbarker (Dec 23, 2009)

Hi fellas-
Great forum you have here. 
Anyone figures this one out, and you have my utmost respect:
I have a Ruud 90 plus furnace running on propane, installed in the mid 90's. Seems like I have a problem with insufficient draft.
Draft inducer kicks on when thermostat calls for heat, but it does not generate enough vacuum to close one of the pressure switches. Obviously, the furnace sequence stops here. The hot surface ignitor never heats up. Draft inducer shuts off after about 2 minutes. It repeats this cycle a few times and then gives up. The draft inducer seemed to get a bit too hot when it was running, so I replaced it with a new one. Problem persists. I check exhaust vent EXTREMELY thoroughly, to the point of actually cutting apart the PVC pipe to visually inspect every inch for possible obstruction. Vent was clear. It is now properly reassembled. 
This furnace has 2 pressure switches. One appears to be plumbed into the heat exchanger. This switch closes appropriately. The other pressure switch is plumbed into the housing on the draft inducer fan. This is the switch that does not close. It DOES close when a slight vacuum is applied to it manually. I confirmed this with ohm meter. The port on draft inducer housing that the pressure switch plugs into is clear. There are no holes in the tubing that runs to pressure switch. The port on the draft inducer fan that pressure switch hose connects to is not clogged.
So...if you're still with me here...
I put a manometer on the port on draft inducer housing, and it is only generating about 3/4 " WC of vacuum. The pressure switch that is not closing is rated to close at 1.11" of WC. So clearly, the switch is not at fault. This system is simply not generating enough draft. But why? I'm stuck. Vent is clear. Draft inducer is brand new. It IS moving some air, as I can feel it briskly moving out of the exhaust vent outside. By the way, I do have a woodstove in the house. Someone suggested that perhaps it was creating a huge negative pressure in the house that the draft inducer could not overcome. So I let the stove burn all the way down. Opened a door in the same room as the furnace, and problem persists. 
Thank you in advance for any help you can offer.
-Jay


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## jbarker (Dec 23, 2009)

Forgot to mention- I have confirmed that I am getting 120 volts to the draft inducer.


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## yuri (Nov 29, 2008)

Did you check the INTAKE pipe, not the exhaust pipe? Propane can burn dirty and you may have a partly plugged secondary heat exchanger or a cracked heat exchanger.


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## jbarker (Dec 23, 2009)

Thanks for the reply Yuri.
I am quite sure that it is the exhaust pipe that I checked. That is a good question to raise though.
I don't think the heat exchanger is cracked, as we have not had any CO problems. Also, the flame pattern on the burner doesn't change when the blower fan turns on. I did wonder about the possibility of clogged heat exchanger. I didn't know how common that is.
Please correct me if my logic is faulty, but the way I look at it, to get sufficient draft, you need 3 things:
1. no exhaust obstruction
2. no intake obstruction
3. good draft inducer fan

This may be an oversimplification, but if this is correct, I have eliminated 1 and 3, leaving intake obstruction (clogged heat exchanger) as the logical problem.
Is this common on propane fired furnaces?
Can it be unclogged, or am I looking at getting a new furnace?
Thanks for you insight. Merry Christmas.
-Jay


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## Tator1076 (Dec 22, 2009)

You need to pull all tube to draft motor and heat exchangers. That a paper clip and clean out the holes. You have crap in one of those ports and need cleaning. If you had crack or plug heat exchanger it will trip roll out


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## JohnH1 (Jan 9, 2009)

Make sure the drain trap has water in it. It will not pull a good vacuum with water in it. Also confirm the gasket behind the Induser is in place. Will the switch pull in with the exaust pvc disconected? I am assuming this is a older istall and the vent is within venting distance guide.


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## jbarker (Dec 23, 2009)

Gasket behind inducer is in place. Vent pipe is the same length as it has been when it was installed professionally about 13 years ago, so this should not be an issue. Thepressure switch does pull in when the exhaust is disconnected. However, I don't think that this necessarily proves there is an exhaust obstruction. (Actually, I know for a fact there is no exhaust obstruction after close inspection). My understanding is that there are 2 loads on the inducer: the intake restriction and the exhaust restriction. By changing the exhaust restriction to zero, the draft inducer is able to create enough vacuum to close the switch, even with the (presumably) partially clogged heat exchanger in the circuit.

Tator- I have already checked all ports, and none are clogged. My original post was quite long, so many people probably missed this- But the draft inducer is simply not creating enough vacuum to close the switch. I checked by placing a manometer directly on the port on the draft inducer housing. It is only creating 3/4" WC of vacuum. Switch is rated to close at 1.11" WC of vacuum.

I am all ears to more suggestions, but I suspect Yuri is right about clogged heat exchanger. Now I just need to find out if this is a fixable problem. Let me know what you think. Thanks everyone.
-Jay


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## JohnH1 (Jan 9, 2009)

Simmiler to the plugged heat exchanger the secondary exchanger could be flooded maby due to a plugged drain.


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## yuri (Nov 29, 2008)

A clogged intake pipe is a different issue than a flooded or clogged secondary heat exchanger. There may be a screen where the intake pipe attaches to the furnace or burner box. Rheem/Ruud usually won't light properly with the burner box cover off.


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## jbarker (Dec 23, 2009)

Gentlemen,
I neglected to mention that I did check for a clogged drain/water backup and there is no problem in this department. 
As for the intake, it has a screen over the opening of it outside. So I know that there is no varmint in there, although conceivably there could be a beehive or something in it. Although I did not cut the intake pipe apart to check every inch of it, I know there is no obstruction in the first or last several feet of it. This furnace has run fine in the past when I had the access cover off it. I do not suspect that the intake pipe is the culprit here.


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## 3 legged dog (Dec 21, 2009)

Is it possable the induction blower wheel is loose, or coverd with dust?


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## yuri (Nov 29, 2008)

I had wasps build a nest on the intake of a Lennox G26. Summer ended, wasps went South. Nest dehydrated and shrunk. Furnace fired up in early October and nest got sucked in. Never say never. If you cut the intake pipe off a foot or 2 B4 the furnace and it runs OK, the pipe may be blocked. Use a plumbers MJ/Fernco rubber coupling to reattach it.


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## jbarker (Dec 23, 2009)

Well, that was easy enough to try, so I gave it a shot. No change in the problem after I cut the intake pipe.
3 legged dog- The blower wheel is not covered in dust, as it is brand new. I know that it is secured to its shaft, as it does produce an exhaust draft. Just not strong enough.
I appreciate your advice everyone. Have a great Christmas today!
-Jay


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## beenthere (Oct 11, 2008)

Is this one of the drum units?


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## jbarker (Dec 23, 2009)

I'm not quite sure what you are referring to. If you are referring to the inducer itself, here it is: 
http://www.amazon.com/gp/product/B000BV22SG/ref=ox_ya_oh_product


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## yuri (Nov 29, 2008)

Post some pics of the furnace with both doors off so we can recognize it.


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## beenthere (Oct 11, 2008)

jbarker said:


> I'm not quite sure what you are referring to. If you are referring to the inducer itself, here it is:
> http://www.amazon.com/gp/product/B000BV22SG/ref=ox_ya_oh_product


No, the heat exchanger style. Rheem early 90% were drum style. And they had problems with them not holding up.


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## jbarker (Dec 23, 2009)




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## beenthere (Oct 11, 2008)

Do you have A/C with that furnace also?

If so. The coil is probably dirty.

Thats not one of the drum units.


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## jbarker (Dec 23, 2009)

I had some trouble getting the pictures posted, but I think the following links will take you to photobucket account with other pictures of my furnace.
http://i128.photobucket.com/albums/p199/nbarker2/102_0853.jpg

http://i128.photobucket.com/albums/p199/nbarker2/102_0851.jpg

Thanks.
-Jay


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## yuri (Nov 29, 2008)

Nothing special about that one and I have seen lots of them. Did you take the condensate trap off and flush it with hot water and Javex/Clorox bleach? May be partly plugged with algae/scuz :sneaky2: and slow draining.


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## jbarker (Dec 23, 2009)

No AC with this furnace.


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## beenthere (Oct 11, 2008)

By those pictures you don't have A/C.

The secondary heat exchanger may be dirty. You have to pull the blower to see it.


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## yuri (Nov 29, 2008)

Check my post below your post with links. Dirty condensate traps are a common problem.


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## jbarker (Dec 23, 2009)

The black pipe to the left of the blower has been perfectly bone dry every time I have taken it apart, (and that has been alot over the past 4 weeks). I don't think that a clogged drain is the problem.
To re-hash things, I have a clear inlet and exhaust pipe, new inducer, have confirmed the port on the inducer is not obstructed, and the inducer only prodeces 3/4" WC of vacuum, when it needs to produce a minimum of 1.11" WC to close the pressure switch. Thanks again for your continued interest.
-Jay


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## jbarker (Dec 23, 2009)

When I pull the inducer, I have access to a hole in the heat exchanger about 2" in diameter. When I look in there, it looks clean, but I'm not sure if that really means anything. 
Does a dirty secondary heat exchanger LOOK dirty, or is the problem deep inside? 
If it is clogged up, is there a way to clean it, or does it need to be replaced?


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## yuri (Nov 29, 2008)

On most units you can remove the collector box where the inducer fan attaches and inspect the tubes which spill into the collector box and drain for black scuz (carbon) from the propane. There may be turbulators in the coil tubes and they may be dirty. Only way to know is to remove the collector box and visually inspect the secondary coil tubes. Buy a new gasket for the box B4 you take it apart and put some red rtv silicone on the new gasket when you install it or you may get water and vacuum leaks later.


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## beenthere (Oct 11, 2008)

First. what are you using to check the pressure?
A digital manometer, or a water tube?


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## Marty S. (Oct 31, 2009)

Jay, have you called the supply house where you bought the inducer or a tech support line? I have seen other furnaces spec a different pressure switch when the inducer was replaced. Not saying that's the problem but it is worth looking into.


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## Mike in Arkansas (Dec 29, 2008)

Did you buy the inducer from Amazon? Might try an OEM part if so.


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## yuri (Nov 29, 2008)

That is true. I had a aftermarket inducer (Rotom) with 50 less rpms than an OEM on a Ducane and it would not work. OEM is sometimes the best.


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## jbarker (Dec 23, 2009)

I am using a water tube to check pressure. I suspect it is fairly accurate. When I checked manifold pressure, which is spec'd by this model furnace to be 10" WC, it measured dead on at 10".

So, I did buy the part THROUGH Amazon, but not really FROM Amazon. It was purchased from Electric Motor Warehouse. I compared both original fan and new fan. They are exactly the same. Both 1750 RPM. Both .75 amp. Both made by Fasco. I think the reason the new one isn't working is that I jumped the gun on presuming there was something wrong with the original fan to begin with. I have not yet spoken to tech support. I don't think this supplier actually has a tech support.
I do have reason to suspect the draft is insufficient. Let me provide more info:
6 weeks ago, problem started with flame not traveling down all seven burners. Obviously, flame sensor detected no heat, and then gas valve would close after a few seconds. Draft inducer ran a few more moments, then shut down, and cycle would repeat. This problem was intermittent. Given 2 or 3 attempts, flame would eventually propagate properly across the burner. I checked all orifices. All were clean. Pulled burner, found no major obstruction, cleaned it anyway, and problem persisted. At this point, once the burner lit, the furnace would run until thermostat was satisfied. A few weeks later, however, furnace would shut down before thermostat was satisfied. There was no flame rollout. Manifold pressure would instantly drop to zero as measured on manometer and burner would shut off. I suspect the limit switch was tripping. Poor draft, not pulling enough exhaust out, heat exchanger overheated, furnace shut down. Now, as you know problem has worsened to the point where furnace doesn't run because draft inducer doesn't pull enough vacuum to close pressure switch.


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## jbarker (Dec 23, 2009)

Forgot to mention, I tore this furnace down pretty far a few weeks ago. Stopped short of actually removing the heat exchanger, but I did not see a way to pull the plastic front piece off the heat exchanger. I guess I should take a closer look. Anyone know for sure if there is a way to get in to clean secondary heat exchanger on this model?


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## zootjeff (Jul 11, 2007)

jbarker said:


> Forgot to mention, I tore this furnace down pretty far a few weeks ago. Stopped short of actually removing the heat exchanger, but I did not see a way to pull the plastic front piece off the heat exchanger. I guess I should take a closer look. Anyone know for sure if there is a way to get in to clean secondary heat exchanger on this model?




Is your draft inducer housing filling up with water? If you pull the plugs is it clean? If you had water from the combustion or draft inducer building up, it could cause this problem. Are there other flexible hose take-offs on the inducer housing? The one you have it hooked to could be prone to water pooling. Isn't that where they normally connect a tee to the condensate drain? I'd think you'd want the pressure take off higher up on the blower housing.

Also is that the same place the old inducer took off for the pressure switch? Looks like that is the high pressure side of the inducer, not the low pressure side. Low pressure is on the inside of the squirrel cage.


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## yuri (Nov 29, 2008)

The manufacturer/design engineers are looking for a pressure differential across the exchanger. They decide where the ports are on the fan. Sounds like the exchanger is quickly plugging with soot.


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## jbarker (Dec 23, 2009)

Yuri-
I agree with you. After you mentioned the possibility of plugged secondary heat exchanger, it seemed like the only logical cause of the problem. Is this something that is typically repaired, replaced, or just get a new furnace? Thanks so much for all your help.
-Jay


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## yuri (Nov 29, 2008)

I don't do a lot of Propane but have heard that is not uncommon to foul up the exchanger. I did several thousand posts at defunct HVACMech and other people have had your problem. Propane is hard to burn clean and the soot/carbon mixes with the condensate/condensed water. Looks like you would have to replace the heat exchanger or find a Pro who can dismantle it and clean it. Probably cost $600-$1000 to do so. If it is mid 90's then I would replace it. We never clean heat exchangers as it would require some kind of chemical flushing etc and would cost a fortune. It may also crack soon or have other problems and be a $$ pit so I would go with a new furnace. And make sure it is properly checked and setup by an experienced Propane tech once a year. Lots of techs work on Natural gas but only a few are good at Propane or have the necessary experience. In my area the Propane supplier has techs which are good.


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## beenthere (Oct 11, 2008)

Propane is a dirty fuel. But most of the problems come from lack of proper set when installed. And from lack of maintainence.


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## JohnH1 (Jan 9, 2009)

In the picture I can not tell but it look as if there is a drain from the exaust vent positive pressure. ties directly to the drain off the heat exchanger a negative pressure. Could the positive be blowing into the negitive side causing the lack of vacuum?

Edit
Nevermind they look like They are seperate. Make sure the trap has water in it.


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## jbarker (Dec 23, 2009)

Thanks for all the info Yuri. Your insight has been invaluable.

Beenthere: When you refer to "proper set" - is there anything to be set properly besides inlet and manifold pressures? I mean, of course you need to have proper size orifices in the manifold, and spring in gas valve needs to be replaced with one for propane. But I wasn't sure if there were any other factors that I am overlooking.


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## beenthere (Oct 11, 2008)

Temp rise. Too cool, and you get condensation in the primary heat exchanger.
Too hot, and you get fatigue in both heat exchangers.

Next, combustion should be checked. To know if its burning correctly. You can have factory speced manifold pressure. And still be burning dirty, or too clean. Hard to tell by just manifold pressure and temp rise. The length of the vent and intake have a big effect on that.


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## oldguy2 (Jan 14, 2009)

*inducer motor*

i once replaced a inducer motor. and furnace wouldn't run. finally figured out that it didn't seal on furnace plate good enough. i would apply pressure with my hand on inducer and furnace would fire up. so i sealed the inducer with a gasket along the edges of the inducer motor. furnace finally fired up. furnace was an aireflo model.


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## JohnH1 (Jan 9, 2009)

Has the issue ever been found on this?


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## jbarker (Dec 23, 2009)

Never was able to find a satisfactory answer to why this thing wouldn't run right. Tore it all down, removed heat exchanger, separated the primary heat exchanger from the secondary. It had some debris in it, but not a ton. It wasn't what I would call clogged up. I decided to get a new furnace.
Bought a Rheem 95%, 105,000 BTU. Appears quite similar to old furnace. I installed it this past weekend. It is now up and running, but I will continue to use wood stove primarily until I am satisfied that it is set up properly. Thanks again to everyone for your help. I have found this experience very interesting and I have learned a lot. This has been a good reminder to me that "the more I know, the more I realize how much I don't know".
-Jay


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