DIY Home Improvement Forum banner

Perplexing problem, Ruud furnace

17K views 43 replies 10 participants last post by  jbarker 
#1 ·
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
 
See less See more
#4 ·
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
 
#6 ·
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.
 
#7 ·
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
 
#9 ·
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.
 
#10 ·
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.
 
#12 ·
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.
 
#13 ·
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
 
#17 ·
#21 ·
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.
 
#25 ·
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
 
#26 ·
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?
 
#27 ·
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.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top