Ducane furnace can't keep up

Don't overcomplcate it. Air needs to flow freely through the tubes. Wrap your mouth around the end of each disconnected hose and blow. If air does not travel freely, figure out why because it is causing the problem. That plastic trap at the bottom too, they must all be clean and clear.

 

Remove hoses completely - both ends. Then you can use a compressor if you want but might be overkill. Don't use a compressor with one end still attached as you can destroy pressure sensors and other equipment.

 

so I did a couple of the tests today on a day trip. I pulled the hoses off of the condensate trap. I did notice that when I blew into the trap, that there was a lot of water, and bubbling when I did that. It was pretty interesting. I was able to crawl back behind the furnace to trace where the drain is going. So there is a condensate pump in the back where the trap housing will drain into. So the one thing that I thought was interesting was that the pump didn't come on. When I was blowing into one of the ports on the trap, I could hear that it was bubbling in the pump. I'm not sure how much water it takes in the pump for it to kick off, and start pushing water out. The one thing I didn't do while I was out there was pour water into the pump, and see if the motor kicks off. It is a very tight spot back there, so it is very hard to work. The pump is a Beckett CB151UL. I'm trying to figure out if the pump is even working.

 

It is pretty common for condensate pumps to fail. If the the condensate does not drain the level can back up into the inducer housing and the operation of the pressure switch can be effected. When you have the hoses off, you can take them to the sink and flush them out. The condensate is nasty stuff, and can also leave residual buildup in the hoses, and eventually on the inducer wheel, which will cause it to become imbalanced. This causes vibration of the unit and can greatly shorten the life of the inducer motor. It is pretty common for the hoses to be deteriorated and need replacement also.

You could have tested the furnace by clearing the hoses and allowing the condensate to run into a pail for a few heat cycles to see if the problem is still present or not.

 

Yeah, the main reason that I didn't pour a cup or 2 of water into the pump was that I didn't have a spare pump sitting on the side if that was the problem. I thought I would be making the problem worse by filling up the pump tank. Also, since I didn't see a bunch of water come out of those 2 hoses shown in the picture above, does that mean that the pump is probably working. If it was completely broken, then I would think that water would be filling up in that line, and I would have gotten a lot of water coming out. The fact that when I put a straw to the port of the hose coming from the inducer and blew; and I could hear water percolating in the pump...may mean that the pump is fine. I was so hoping that the pump would be the problem. If the pump was completely broken, then water would be backing up everywhere. If the pump was not keeping up, then maybe I would see slow performance, that could account for what is happening.

 

If the furnace is not running normally it will not create condensation like it would on a regular cycle. The condensate must have a clear path to drain from inside the inducer housing to the outside of the furnace. If there is a floor drain, it is much more reliable than a condensate pump.

 

So I see a couple of things I need to test. Pour water into the pump and see if it kicks off. THe other test was maybe to have the inducer hose got to a bucket got s quick 20-30 minute test to see if that keeps it out of error mode. I was also looking at a mamometer. I see them online for 38$. I can put that on there, and see if I can tell when it drops to a rate that opens up the sensor.

 

Be glad to have the favorable temperatures that you have there. It stays below freezing most of the winter here, so having the furnace working properly is what keeps the pipes and the peeps from freezing solid.

 

So I ordered a manometer and a wire snake that has a camera and a light that I can try to see if there is blockage in either pipe going down to the furnace. I have to make some traction on this, or I'm going to start bringing service guys out to see what they can figure out.

 

I have a hose/testing question. I received the manometer last night, and I'm trying to make sure that I have the right hoses and conectors for the test. My tester has 3-4 small clear hoses that will fit over the port that the tester has. I am trying to make sure I can test the hose that comes from the PS and goes to the trap(shown in picture). I think I will just need a "t connector with barb connections", which I'm heading to grangers later today. I did some light searching about getting spare hoses to complete the test. My thought is that I can take the hose coming from the PS, and put it into the T, and then get one hose from the trap to the T, and then use one of the hoses that my meter came with to complete the T? It seems pretty straightforward. I see some folks talk about using hoses from auto-parts stores. I'm also going to see if grangers has hoses that will work. I also wanted to replace the hose form the inducer to the trap, but wasn't sure the best way to replace that. That hose has a built-in elbow, and then comes down about 10-12 inches. Is this something that I could purchase at an auto parts store, or is there a better way to select a hose for that application.

 

The pre-formed hoses are best ordered from a heating/cooling supplier from the factory parts listing. The small vacuum hoses, tees, and splices can be found at auto parts stores. We have Grainger here, but most items there are catalog orders.

 

So I did a few tests, and here is what I discovered. I did pour water into the pump, and that seems to come on and work okay. So that is ruled out. I did put the manometer and "T" connector into the system. I watched as the pressure number really bounces around. It started off around 2.6-2.9..and then after a few minutes it started to dip down to 1.7.2.0. Even a while longer (maybe 7-10mins) and the number started to get down into the 1.6-1.9 range. The pressure sensor is set to 1.71) So it basically just kept slipping down, and the meter seems to keep bouncing. I'm guessing that this is not a good sign. It seems like the burner runs for a while (3-4 minutes) and then just cuts off. I'm not sure how long the burner should run in a normal situation to heat the house, versus a "bad" situation. It seemed like it stayed in normal mode, and would light the burner, and then go off, and on for serveral times...before it goes into error mode. I"m not sure what to make of all the data points. I had a problem with my new wire light camera, as the light wasn't very strong. I couldn't do the exhaust line check, and the input line check.

 

The basic heat cycle is -

1. The thermostat calls for heat. 2. The inducer fan turns on. 3. Pressure/vacuum switch activates. 4. Gas valve opens. 5. Ignitor on.
6. Burner Fires. 7. Flame sensor active. 8. Ignitor turns off.

As long as these conditions are present, the burn will continue indefinitely until thermostat is satisfied.
If the pressure switch opens, or the flame sensor does not stay active, or the over-temp switch activates, the gas valve will be turned off prematurely.

If the pressure switch is staying on but the burner goes out, try cleaning or replace the flame sensor.

 

okay it seems like you been able to help me narrow this down. So it definitely looks like that could be the problem. I need to do that extra test of putting a multimeter up to the switch to make sure that it is seeing 24 volts going through.

 

So here is the top section where the burners are. I believe that the sensor is the part where the yellow wire is going. It looks like a lot more has to come out to get to the sensor to try and cleaning. Maybe it is worth getting a technican to do that removal for cleaning, and possible replacement. Am I missing something that will make the removal of the sensor easier?

 

Do you have the manuals for this thing? A flame sensor (there's more than one type) generally either outputs a milliamp level voltage dependent on the temperature (thermocouple type), or it changes resistance based on the temperature (thermistor type). The manual should tell you how to test that. If it isn't in the normal range, then, cleaning, repositioning, or replacing is called for. If that's changing as the burner comes on, and the system fails to stay on when calling for heat, the logic board may be bad or a connection is bad.

 

I do not have the manuals for this. This look
s like it is 10-12 years old (based on home inspector report). It would be good to have the manuals. I even tried to order that hose from the inducer to the Trap..and the one company "Shorty HVAC", the don't even carry stuff for this particular model/SN. So I have noticed that it seems that the system is working better. It is still not 100%( as I see that it still goes into error mode). So the temps in Delaware have been pretty warm, so I haven't had a good baseline test like I had several weeks ago. The only real thing I have changed is the vacuum hose a: some hose clean out, b: new hose from pressure switch to trap(the hose on one end looked a little elongated). My plan is to see when the low temps drop to 30degrees by end of the week, if the system does a better job of keeping up. I am still going to have an HVAC guy come out for the check out of the flame sensor. One additional update: Since it looks like the burners have no problem lighting, I don't see a problem with the call for heat. It will jsut run for a while, and then cut out. It seems like it will do that 3 times, and then go into error mode with the lights, so I hoping it is not hte control module.

 

On the inside panel somewhere in the thing, there should be a schematic. While they are somewhat cryptic, with some study, you should be able to follow the interlock circuit, and isolate where the problem is, if it's in an interlock/safety device. Do this at your own risk while closely observing, but if you find an interlock that is not closing, you could bypass it temporarily to see if things stay on. You'd need to determine then if the interlock, either via a sensor plug/hose/wire, etc. was bad, and the actual symptom was good, or the sensor itself was bad, or the signal was good going into the control box, and then the control box was not acting on it properly.

Have you searched the manufacturer's website to see if you can download the manuals? If not, have you called them to see if they could send you a PDF or maybe even a hard copy? It's hard to troubleshoot something until you understand how it's supposed to work...prior to that, it's guessing...maybe educated guessing, but easy to miss something.

 

Thanks for the input Jim. I have setup to have an HVAC guy come out and troubleshoot the specifics of the problem. I've noticed something quite strange "remotely" via the Nest. It seems that when I set the "eco-low mark" temp to 60, it seems to keep up and not go into errotr mode. The only reason that I know that it hasn't gone into error mode is that when I check it frequently, it shows it running, and shows it off, which means it is maintaining the temp. Even today when the outside temps are low 20's, it is doing the same thing. As soon as I raise the temp setting to 61, 62: it seems to go into the death spiral, and never keep up. I was thinking maybe the Nest is somehow malfunctioning...but all it really does is send a call for heat. I could see if the Nest wasn't calling for heat, and the nest temp is below what I set it at..then that would indicate that the Nest is messing up. But any time the air temp is below the "set" temp, I see the Nest doing a call for "heat". So the other thing I was thinking that maybe something is getting hot (inducer, heat exchanger), and that is kicking into the limit or something to have it back off. The strange thing is that I would think the 60degree mark would slide down to 52-55 when the outside temps dip like they did last night. I don't see any change on what the system will maintain. It occurred the same way when the outside temps were 32-40, as it is today when the outside temps are 22 this morning. Very consistent.

 

So the HVAC guy came out today and did a few tests today. He feels pretty sure that there is a hole in the heat exchanger, and that is what is causing my furnace to go out periodically. He thinks that once it heats up, it is cutting the rollout switch. He was trying to show me that the burners, and showing how the once section is not burning correctly. He was trying to show me the difference in a flame pattern (roll out flame) between the one burner and the other. It is hard for me to see, but I just don't look at it enough. He also said that the code was four blinks, which is combustion air blower is energized. So I'm trying to decide if I want to do a heat exchanger, or the whole furnace. The only reason that I would consider doing just the exchanger is because we want to do a big remodel of this house in 4-5 years. I know that if we do that, we would have to re-spec the furnace, and would probably have to get a new furnace to support the new requirements. I am waiting to see what the cost of a new heat exchanger, and a new furnace.