Gas and Oil Home Heating Furnaces - Furnace not keeping up...

Equipment involved:

The following were installed 10/5/89:
Furnace - Williamson Natural Gas Forced Air WU47072N14
Filter - Williamson Electronic Air Cleaner SLM-14
Humidifier - Aprilaire Humidifier model 440

The following was installed spring 2004:
Thermostat - Honeywell CT-5500

House:
Located in SE MN. 2-story with full basement. Each floor is in the neighborhood of 700 sq.ft. Thermostat is on the ground level.

When the outside temperature drops below 0 F, the temperature in the house drops as well. When it is about 0 out, it won't get any warmer than about 67 in. If the temps out are above 0, inside is where ever we set it.

What I have checked:
The thermostat is currently set to run at 72. It shows that it is set to heat, and there is a flame icon indicating that it is calling for heat. The furnace has three burners, all of which will ignite and have a solid blue flame with ocassional orange tips. The burners will ignite and stay lit for about 50 seconds. The burners then go out and stay out for a few minutes before igniting again. We have been in this house for just over 6 years, and this started to occur last winter, but only on the coldest days, and then inside temp would stay closer to 70. The thremostat was replaced this past spring when having some problems with the central air. Heat would come on, air would not. The repairman suggested a new thermostat, which I purchased and installed, before he finally found a wire that was shorted out as it went through the siding to the AC unit. Not sure what check or try.

Thanks for any suggestions,
George

Hey George,

I am from Rochester, so yeah we've been having our cold spells. Where in SE Mn are you?

I have not been around these newer Williamson, just the old ones when my Dad used to install these.

Only thing I can suggest for now, is try to remove the t-stat from the sub-base, and jumper the R and W wire.

See if the system stays running the whole time.

If it still doing the same thing as before, then it's something inside the furnace.

I am not able to pull up the model #, is this a 90% (PVC Vent) or 80%?

If it's 90%, check your pipes outside of the house to make sure it's not blocked up with ice.

What type of ignition? (Spark, standing pilot, Hot Surface ignitor)

I'm in Rochester also. I tried jumping the R + W wires, and it does the same thing. It is PVC vented, and, FWIW, one piece of literature the previous owners left says it "Delivers up to 95.8% Fuel Efficiencey". The vent outside is clear. There is a pile of ice forming on the ground, but I don't think that would be a problem. Don't know your thoughts, but Steve Green did the install. I've had him out, and wasn't impressed. Anyone else you would recommend if I need to have it serviced?

BTW, my guess is it is a spark ignition. There is no flame, until it ignites. Then it ignites from a central point and spreads to all three burners.

I just brought an older house a few months ago, and Green did the A/C install here.. I wasn't impressed with it.. Anyway I had to put in a new furnace, and I had HIMEC do the install while they were here, I had them take out the A/C and put in a new one in.

ANyway.. If it's trying to spark, and no pilot after it sparks, sounds like the pilot valve on the gas valve isn't opening for you.

Give HIMEC a call, 288-7713

Stay warm tonight!!!

Well, it does spark, and there is a pilot after that. Then the three burner ignite. The flame is there the whole length of the burner, but it only stays running for about 50-55 seconds. Then goes out for the next several minutes and repeats. Hence we get flame at the burners for about 15 minutes out of every hour, and the house gets a little colder. It is -5 outside this morning and 64 inside. Brrr. I may have to give HIMEC a call to see what they can find, unless someone else has any suggestions.

George

Try cleaning the flame sensor with some fine steel wool.

Hey George,

What've you come up with?

Keep us posted.

Merry Christmas to you and your family!

I looked through the technical manual that came with the furnace, and cannot find the flame sensor listed, so am not sure what to try on my own. I'm planning on calling someone in next week. I'll let you know what I end up finding out.

The temp inside has not dropped below 64. It's a bit chilly, but can be dressed for. And, since the outside temp is forcasted to increase, I expect the inside temp to do the same.

Thanks for the advice so far.

I think I have the exception. When I watch it fire up, I hear a spark, then see a pilot light, then the three burners light up. The schematic shows a spark wire and a pilot burner. Inside on one of the stickers, it says that the appliance is equipped with an intermittant ignition device. On the electrical schecmatic, I see an ignitor sensor that is in the circuit with the spark wire. I don't think this would be the problem since the pilot ignites, the burners ignite and stay running for about 50-55 secs everytime they ignite.

And yes, I think it has had the same duty cycle all along, and that it is only noticable when the temps drop outside. The temp has climbed into the 20s today, the duty cycle is remaining the same, and the temp inside has risen to 70.

How would one go about testing a limit switch? I can find it listed in the parts diagram, and can find it on the furnace. It has two wires attached to it, and there is one screw holding it in place. It would be very easy to replace it, if I could get a hold of a replacement.

I would guess it is not a two pipe system, as the only pipes I can see connected to it is the one for the gas line and the pvc for the exhaust. There are three burners and directly above each one in the top panel is a 2 3/8" hole.

Thanks again,
George

I was reading through the installation manual for the furnace and saw a section titled "Check Temperature Rise". In the sections there is the statement "If the correct amount of temperature rise is not obtained, it may be necessary to change the blower speed. A higher blower speed will lower the temperature rise. A slower blower speed will increase the temperature rise."

It then goes on to indicate how to change the blower speed. There is a terminal block with 5 terminals COM, HI, MH, ML, LO. There are three wires that are connected to the block W, V, Y. The white wire is the common. The violet wire is for the cooling blower speed and the yellow wire for the heating blower speed. It indicates that the blower speed for cooling should be set to HI. The blower speed for heating should be set to achieve the correct temperature rise (35-65 degrees).

When I checked the main junction box the cooling blower speed is set to ML and the heating blower speed is set to LO. My question is this: If the blower speed is too low, could that cause the temp in the main heat exchanger to rise above the 190 degrees set as the top limit for the limit switch? And if so, would this cause the burners to cut out? Is there any possible problem that could occur if I set the blower speed to MH as is shown in the electrical diagram for the default setting?

I am tempted to try it making the assumption that the manufacturer would not allow a blower speed that would damage the blower, and I can't think of any other possible problems. I am waiting, however, to get another opinion.

George,

Did you take a temp reading to see what the temp rise is?

You can change any speed on that blower for heating and cooling.. Just as long you stay in the "Safe range of rise" for heating..

For cooling, you can go slower to help cool/dry the air better. High is going to move more air if you have a large home that needs to get the cold heavy air upstairs.

But take a reading to see how hot it gets when the burners just turns off on you.

I am off Monday if you really really want me to come over and take a peek.

Well, I went ahead and tested the different blower speeds, and there was no change in how long the burners remained lit. So, there goes that theory. I put all the connectors back where they were when I started. I will try calling around tomorrow to see if I can find someone who will sell me the part I need.

Now, just a point of clarification. This funace has a fan and limit control that appears to be all one unit. It has a bar that is about 6" long that sticks into the primary heat exchanger area. I am assuming that is the limit switch. Would that be correct? It also controls how long the fan stays on after the burners cut out. The fan control is able to be set in the range of 90 - 120 degrees. From what I see, I would either need to drill out some rivets, or replace the whole thing. Does that sound right?

Well, I pulled the control out this morning to see if I could find any identifying marks on it to use to order a new one. I also measured the part that sticks into the heat exchanger and that was 6 3/4" long.

The numbers I found were:

HQ1002743CS
FALTS57C-13T-120-170
24V, HTR
4686
LIMIT 170

The part nubmer listed in the technical manual is 1002743. Does it sound like the information I have here should be enough to find a replacement, or do I need more?

BTW, in an earlier post, I said the limit was 190, but I must have misread something because all I can find now is 170, which matches what is in the furnace.

George

Alls well that ends well. It was a CamStat Limit delay control in my furnace. I was able to find one of the HVAC repair shops that would sell to the public, after a couple of rejections. They charged me $60 for the new part. It took me about 5 minutes to install it. Turned the furnace back on and it fired up right away. The burners were lit for a full minute before the blower kicked into HI speed. Not sure how long the burners ran for, but it eventually settled into a cycle of 1 min on, 45 secs off. So, more heat than cool. The ductwork right by the furnace now feels hot to the touch, and I can feel heat coming out of the vents in the 2nd floor (didn't feel that before either). I think I will need to adjust the blower speed to run a higher speed to keep the burners from starting and stopping so much. That will be a task for tonight. Amazing how much you can learn about a furnace if you want to. Thanks for all the help.

George,

How's it working out so far?? Still short cycle??

WHo did you end up getting the part from?

It's still working out well. When there is a call for heat from the t-stat, it still falls into the short burn cycle, but the call for heat eventually goes off and the fan and burners go off as well. Then the house is quiet. I can live with the way it is running.

I ended up getting the part from K&S. Very good to work with, and no hassels about selling to the public like I got from HIMEC and Tonna. Tonna would not sell to me, but referred me to K&S. HIMEC said they would look into what part I needed and call me back, but they never did.

Later.

The short cycle on the burner isn't good.. Is it going off on the high limit? If so, check to make sure you have good air flow..

check make sure..
-air filter is good
-return vents are not blocked
-Supply vents are open
-blower maybe caked up with dust over the years?
-A/C coil not plugged up, cause the air flow to drop.

I think I'm having the same problem as the person that started this thread. I also live in Minnesota, perhaps that's the true problem :wall:

Furnace is about 18 years old. I have an electic start pilot that comes on at the first or second click, that seems to work. Then the burners kick on fine. But after about 8 seconds they go off. Then after about a minute it tries again. After about 7-10 tries the furnance may kick on normally. But its not always staying on long enough. It may only stay on for a minute or two even thoug the house is down to 60 degress (thermostat set at 72). Outside temp is now -5 degrees so I'm getting worried.

From everything I've read today it sounds like a flame sensor. First does this assumption sound correct? Second is there anything I can do to get me through a couple weeks? I'm out of town starting Sunday (my wife will be here and can call for emergency service is needed). I've read here and else where that the flame sensor can be cleaned and adjusted closer to the flame. Where can I find it? I see a panel right above the burners with 4 screws about 3 inches square, with 2 wires going to the back of it. I'm thinking if I unscrew this the sensor may be mounted to the otherside. Does this sound right? It might take several hours to a day or two to get even emergency service with temps down to -20 tonight. So I don't want to screw it up. Any advice? (replies to john at eaglestock.com would be appreciated though I'm going to try to check back here too). Thanks.

Is this a Williamson as well?

Yes, there would be two wires coming from the burner, One is the sensor, and other is the spark..

The sensor would be just a simple rod that the flame hits.. Just sand it down lightly with soft steel wool.

I have a Carrier furnace. I'm pretty sure its the flame sensor. But here's something weird that might suggest another possible cause. When I take the fented panel off (the one in front of the burners) the furnance works much, much better. I'm wondering if maybe that's allowing the flame to burn hotter and thus trigger the flame sensor easier. But the whole panel is vented so I don't see how this could help much. I've put it on and taken it off a few times for testing and I'm 100% sure its making a difference.

The other thing I was thinking is that there is a small fuse of some kind on the flame sensor lead. I think its suppose to detect heat in the control area and shut off the gas. Perhaps its getting too hot in that area. Its never felt hot to me so I'm not convinced that's playing a part here.

I'm not sure if I know where my flame sensor is at. There are no rods sticking in to the burner area that I can find. On the duct box above the burners there is a 3" square panel with two connectors on the back of it. This panel is held in place by two screws. I'm thinking that the flame sensor must be on the other side of this (probably part of it). But since its -10 outside right now (and going down to nearly -20 later tonight), and the furnace is keeping up with the outside panel removed, I'm reluctant to take it apart further (I would hate to break something).

It sounds like you may have a dirty heat exchanger or partially clogged flue or chimney. When is the last time you had it cleaned?

I had the exact same symptoms as you, herronj: furnace kicked on and off every minute or so, it wasn't able to keep up with the thermostat on cold days (the room temperature was lower than the set temp), and when I removed the blower door, it worked better. I have a Heil/Whirlpool NUGK075 furnace, installed in 1987.
I jumpered the two red wires on my fan/limit control mounted on the plenum above the burners (Cam-stat HQ1002743CS), which then bypassed the hi-temp cut-off, and my furnace started working fine, which tells me that the control is bad: it is telling the system it is too hot (over 170F) when it isn't. (I am skipping the dead-end diagnostic steps.) I felt the plenum and it didn't feel that hot, and I had already put in a new air filter, and the blower fan was turning fine, so it shouldn't be overheating.
So, if you jumper the contacts on your limit switch that control the hi-temp cutoff, and it starts working fine, that may be your problem.
I am writing this so that even if this advice is too late for herronj, maybe someone else may benefit.
Kenton

I have a Carrier furnace. I'm pretty sure its the flame sensor. But here's something weird that might suggest another possible cause. When I take the fented panel off (the one in front of the burners) the furnance works much, much better. I'm wondering if maybe that's allowing the flame to burn hotter and thus trigger the flame sensor easier. But the whole panel is vented so I don't see how this could help much. I've put it on and taken it off a few times for testing and I'm 100% sure its making a difference.

The other thing I was thinking is that there is a small fuse of some kind on the flame sensor lead. I think its suppose to detect heat in the control area and shut off the gas. Perhaps its getting too hot in that area. Its never felt hot to me so I'm not convinced that's playing a part here.

I'm not sure if I know where my flame sensor is at. There are no rods sticking in to the burner area that I can find. On the duct box above the burners there is a 3" square panel with two connectors on the back of it. This panel is held in place by two screws. I'm thinking that the flame sensor must be on the other side of this (probably part of it). But since its -10 outside right now (and going down to nearly -20 later tonight), and the furnace is keeping up with the outside panel removed, I'm reluctant to take it apart further (I would hate to break something).

I would not bypass the ligh limit control for anything but brief diagnostics. Some people may get the impression that they can simply bypass the limit and replace it at their leisure, or not replace it at all.

Could it be that the fan limit switch: Cam-stat falts57c-13t-120-170 aka HQ1002743CS is not up to task in certain applications? I have a 1987 HEIL NUGK125DK05 which runs well but seems to be burning out this control. Sometimes, I have to jiggle the bottom wire (coming from the high limit switch immediately above the burners)to get any heat. There seems to be a short (looseness) occuring in the spade connector within the cam-stat and when I touch the wire or move it in around, the furnace immediately fires up. Any suggestions? I have purchased four of these cam-stats and they all have developed the same looseness or short on the bottom #5 terminal. How long do these typically last?