When the heat comes on, it runs fine for 5 to 7 minutes, then the controller starts clicking on and off quickly like it is turning off and on. video attached. It is a Honeywell LBF80B804 furnace. I cleaned the cad cell thinking that was it. Could the nozzle need replacing? Any ideas appreciated. Thanks.

 

Welcome to the forums.

It's an Armstrong oil fired furnace...... LBF80B84 95D12-3A
Honeywell 7184 module.

It sounds like the unit may be overheating. I'm seeing a fan/limit control and a safety switch.
Has this unit been cleaned recently ? It may be plugged with soot.

Representative manual...... Armstrong LBF manual (pdf)

 

Forgive me for attaching my issue to yours, but I'm wondering if we might be experiencing the same issue based upon my own findings and Pete's reply to your original thread.

My Thermo Pride Oil Furnace (OL5-85RDA) started acting up 4 days ago. I was away at the time, and it ran fine for 3 days, but the same issue happened again this morning and I was able to see and hear what was happening. My wife heard a 'thumping' in our ductwork (it's a warm air system). I headed down and heard the Solenoid on my Aprilaire Humidifier clicking ON / OFF about every 5 seconds. I knew that really wasn't the underlying issue, so I turned the Humidifier off. I continued to hear a strange sound within the furnace. I had suspected that the issue was the Blower Motor and more specifically, the Starting Capacitor, so I opened up the back to look at the Blower. I heard a 'thump' and watched the blower wheel 'twitch' - it moved about 1/2". And I watched that same scenario continue about every 5 seconds for a couple of minutes. I even manually spun the blower wheel to see if the blower motor would start working properly, but it didn't help. Shortly afterwards, the wheel started to spin somewhat...but it took a few attempts before it actually started working properly. I had ordered a new Starting Capacitor yesterday, and I knew it was arriving today and I thought that the new Cap might resolve the issue. After this second occurrence in 4 days, the furnace started operating fine again.

The new Cap arrived late this afternoon and I installed it right away. After installing it, I followed the power supply line back to the front of the furnace and was looking at the various connections and saw that the power also ran up to the limit switch assembly. The limit switch on my furnace is the Honeywell brand Switch with the Manual / Auto push/pull button switch on the front (see pic). Just for the heck of it, I pushed the button to the Manual mode and the blower fan kicked-on, which I expected. But when I pulled it back out (Auto Mode), it initially shut off, but then it started the same odd thumping like I had experience earlier in the morning. Keep in mind, the furnace had been OFF for at least 30 minutes, so there should have been no call for the blower fan to turn on. But it was as if it was receiving an intermittent signal (power) to turn on, but it wasn't consistent. I started thinking the issue was now possibly related to the Limit Switch assembly. I decided to remove it from the furnace to inspect, but please note, I've never seem one of these before, so I certainly don't know what to look for. I did, however, observe a piece of debris laying on top of the limit assembly, which appeared to be made of some sort of a metallic / foil material. I'm going to try to attach a picture of the limit switch with this debris. For those familiar with this switch, I'm wondering if this debris could be responsible for the erratic operation I observed with the unit today...? If not, is the operation that I've experienced something that would likely be related to the limit switch?

Thanks for any help / suggestions!

Pete

 

Welcome to the forums.

For those following along..... that black spring-like thing in the metal tube is heat sensitive. It winds and unwinds(turns) with the heat and activates a switch. So that piece of debris I circled could certainly be your problem.
The OP's problem is after it runs for XX minutes.... it starts cutting out. So the problem may be high heat is turning that spring to shut the burner off but I don't think it's a debris problem. I think it may be an airflow issue.

 

Thanks for the quick reply Pete! I'm hoping you're right and that metallic foil piece was causing my issue. Due to my lack of understanding of that switch, I wasn't sure if the foil debris could cause an electrical 'short' within that assembly, but I don't know if that's why you think it could be related to my issue.....? Other than that debris, how did that assembly look to you? I understand that they can be cleaned - did mine look dirty and how is it cleaned?

Now that I have removed that debris, I guess I'll have to wait to see if the issue returns. If it does, would you think the next likely culprit is that limit switch itself?

 

I have never cleaned one of them before. Yours looks fine. There is no lubrication required.

That spiral is a bimetal element. It winds up when heated and unwinds when cooled. It is not electrically conductive. If you pull the cover off the fan/limit control the switch will be seen. That round disc in the center is attached to the bimetal and turns during the heating process. The little metal tabs are settings. They can be carefully adjusted by holding the wheel and sliding the tabs.

The bimetal spiral can stick and cause the switch to not work properly.
That would mean a replacement would be required.

 

Thanks again, Pete!

I think I'll order a new limit switch just so I can have it on-hand in case this issue returns. I'll make sure I can return it if I don't need it / don't install it.
I appreciate the assistance - cheers!

Pete

 

Update....
I was hopeful that the debris I removed from the limit switch was going to resolve the issue, but after 5 days, the issue happened again today; clicking off and on again for several minutes. I'm now more confident that the issue resides within the limit switch itself. Although I had ordered and received a replacement limit switch, I wasn't happy with how it arrived - no box, no shipping protection.....it arrived loose inside a plastic bag and the end of the tube was already breaking through the bag. At a cost of over of $100, I didn't want to take the chance that this unit was compromised, so I requested a replacement which is supposed to arrive tomorrow. I'll install it and report back once I can confirm whether the new limit switch has or hasn't resolved the issue.

 

Well....the new limit switch was installed 11 days ago and I haven't had any more issues with the 'clicking' on & off issue. So, I guess it wasn't the Blower Motor or the Starting Capacitor, but I'm glad I was able to clean the the blower when I was troubleshooting the issue. And now I have a new capacitor to replace the original 25 year old one.

My furnace has always cycled on a few times after reaching the set temperature.....I assumed this was normal to flush the warm air out of the fire box / heat exchanger. With the new limit switch, I'm finding that the blower comes on (usually) 2 more times after reaching the set temp, but the cycling time seems to be less than before and in fact, the last cycle time has been only about 10 seconds.

I read somewhere that it's normal for the ThermoPride furnaces to cycle on a couple more times after the set temperature has been reached, but I don't know if that's really the case or not.

In any event, thanks for the help / information provided by this site!

 

Your furnace is supposed to heat. When the plenum gets to a certain temperature the fan is supposed to start and stay running until the burner has shut off and the plenum has cooled off.

Is it cycling back on after the burner has shut down ?
What are the set temps.
You may be able to lower the off temp slightly.

 

It's not uncommon for a fan to cycle back on after it & the burner have shut down. With Thermo-Pride having a very heavy heat exchanger & clay combustion chamber, they hold more heat than lighter weight furnaces & the fan cycling is pretty common. Something that might help is to increase the 'fan on' setting by 10* or so. If you do that, make sure you hold the dial still & only move the pointer.

 

Pete & Grady - thanks for the replies.
I meant to say that my furnace blower cycles on a couple of more times after reaching the set temp, not the furnace itself. But now that the new limit switch has been installed, it doesn't seem that the blower is running as long as it used to be during it's additional fan cycles.

The original switch settings were; 90, 125, and 195 degrees. The new switch came with the following presets; 95, 125, and 200 degrees - I installed them as-is.
It doesn't bother me that the blower cycles on a couple of times....I assume it's not anything to be concerned about....?

 

Nothing to be worried about but if you want to decrease the cycles, you can increase the 125 to 135 or so.The settings on these controls are not super accurate.

 

Thanks Grady - I will give that I try if it becomes annoying.