Furnace just quits

josephny

I have a CMF80 LP furnace in a manufactured home controlled by an Ecobee that's giving me (new) problems.

At random times, sometimes after running for 18-24 hours, it stops running as expected.

Troubleshooting results in discovering that if I short the tstat terminals on the furnace, the furnace comes on.

The Ecobee seems to be working fine (no loss of power or connectivity to furnace that I can see).

If I power-cycle (reboot) the Ecobee, it starts to work again.

I can start replacing the transformer and Ecobee, but I thought I should check-in here for other ideas first.

Here is the wiring. The wire colors (as you all know better than I do) are irrelevant to proper functioning, but I include them here for completeness. The terminal colors on the Ecobee, and the 24vac transformer output colors are accurate (I thought maybe the hot and neutral might be an issue).

Am I missing something?

Thank you.

Jamie Hall

Looks like it's wired OK anyway, and if the furnace runs when you short the thermostat terminals or reboot the Ecovbee -- sounds like it's the Ecobee.

HVACNUT

What do you mean by "it stops running as expected"?
What is the setpoint and what is actual temperature when this happens?
Is there an automatic economy setting?
No program?

josephny

The next time it happens, I will make certain that a power-cycle of the ecobee remedies the failure. If it does, I will factory reset and see if that fixes it. If it doesn't, it gets replaced.

"stops running as expected" means the Ecobee is calling for heat, but the furnace is not making heat (i.e., standing pilot is lit but burner and fan are both off).

I have this Ecobee set to hold a setpoint (no schedule) -- higher than the room temp.

I don't know what "automatic economy setting" is. If it is what Ecobee calls the "Smart Recovery Heat Mode" then it was ON. I just switched it OFF. Could that cause this problem?

Jamie Hall

Wait. The Ecobee says it's calling for heat? Try figuring out the two wires at the Ecobee which control the boiler. Disconnect them and try jumping them together (be sure you have the correct pair). Now does the boiler start?

josephny

I am 100 miles away and I just can see that the furnace is not making heat again.

Earlier today I had someone go over and had him jump the tstat terminals on the furnace and that started it up. I did not have him jump the wires at the ecobee, but I will do that tomorrow.

I really don't know if something is not working properly with the Ecobee or with the furnace. I doubt it's the wire between them, but always good to rule it out with your test.

I am also monitoring the power usage and I have been able to determine that the blower uses about 500 wats and from a graph over the past 30 minutes it looks like the blower is coming on and going off, like maybe it is trying to start and then times out.

Does the CMF80 have some sort of a try-try-try-timeout mechanism?

josephny

Now I'm freaking out because it's 11* outside and remotely turning off and on the Ecobee while monitoring the electric usage seems to indicate that the blower starts up (or something starts up) but the furnace is not making heat.

So my whole theory of the problem being with the Ecobee could be wrong.

In which case, I have no idea what the problem is.

And, I can't reach a neighbor to go out and try to troubleshoot it at 10:30pm.

HVACNUT

If you're reading that something on the furnace is consuming watts, then it could possibly be a faulty blower motor,run capacitor, or time delay relay or fan/limit control. 
The burner could be cycling periodically bouncing off High limit. Without the blower motor running, it'll keep doing that until the cows come home.
You need to physically remove the front panel to jump it at the furnace, right? Ask your neighbor to hang around and make sure the fan comes on. 
You really need someone with an electrical meter and a spare 5 minutes. 

josephny

Thank you so much! It's a huge help (in multiple ways) to know you guys are here.

I have remote temp sensors as well as the temp sensor in the ecobee, so it looks like the house survived the night.

I have him going over this morning.

My plan is for him to go over and immediately facetime me (i.e., don't touch anything until we see what, if anything, is running on the furnace).

We will assess what might be running and confirm the pilot is lit.

Here's my thinking on the process:

Short the tstat terminals on the furnace. If it starts up, the problem is with the Ecobee, tstat wire, or transformer.

If it does not start up, the problem is with the furnace.

I'm pretty lost at that point but I suspect what we find running (and not running) at first look will be useful.

Rotating limit switch? Aux blower limit switch? Thermocouple?

He'll have a multimeter and knows how to use it.

Does this sound correct?

clammy

Looks like you may need a jumper between the rh and the RC terminals . The easiest way to elimate if you thermostat is the issue is to just jump the r and w terminal on the furnace if it fires up and starts the issue is your eco bee wiring . All these new types of stats generally really need a common and r wire to operate properly if you don’t have a mim of a 4 wire then run one ,those steal a common usually seem to fail over time or cause intermittence issues which it seems a lot of service guys don’t pick up on . When faced w intermittent issue I always check the low voltage t stat side and jump it out especially w smart stats they have a mind of there own . Peace and good luck clammy

josephny

clammy said:

Looks like you may need a jumper between the rh and the RC terminals . The easiest way to elimate if you thermostat is the issue is to just jump the r and w terminal on the furnace if it fires up and starts the issue is your eco bee wiring . All these new types of stats generally really need a common and r wire to operate properly if you don’t have a mim of a 4 wire then run one ,those steal a common usually seem to fail over time or cause intermittence issues which it seems a lot of service guys don’t pick up on . When faced w intermittent issue I always check the low voltage t stat side and jump it out especially w smart stats they have a mind of there own . Peace and good luck clammy

Thank you.

Yes, first thing I'll do this morning (after checking what is and is not running) is to jumper R-W at the furnace.

The Ecobee claims to make it's own internal jumper as necessary, and I have it fed with it's own separate 24vac power. I am not certain if the neutral wire is on the C terminal, or if that is critical.

My problem is that if shorting R-W on the furnace does not get it to run, my knowledge of the furnace's systems is not good enough to know well how best to proceed.

josephny

UPDATE:

Arrived at location and found pilot light lit and nothing (no burner or fan motors) on the furnace running or making noise (other than the faint pilot light noise).

Shorted R-W on furnace and furnace fired up.

Replaced transformer and Ecobee, making sure that main neutral wire connects to neutral side of transformer and neutral wire on secondary side of transformer (C terminal) connect to C terminal on Ecobee.

Remoted jumper from R-W on furnace, powered up furnace, and the furnace fires up.

Now I have to see if it stays working.

HVACNUT

clammy said:

Looks like you may need a jumper between the rh and the RC terminals . The easiest way to elimate if you thermostat is the issue is to just jump the r and w terminal on the furnace if it fires up and starts the issue is your eco bee wiring . All these new types of stats generally really need a common and r wire to operate properly if you don’t have a mim of a 4 wire then run one ,those steal a common usually seem to fail over time or cause intermittence issues which it seems a lot of service guys don’t pick up on . When faced w intermittent issue I always check the low voltage t stat side and jump it out especially w smart stats they have a mind of there own . Peace and good luck clammy

I believe there's a separate transformer solely powering the Ecobee at Rc and C.
Rh and W only do switching and there's already 24 volts (or should be) at Rh so we don't want 2 transformers butting heads. 

josephny

Bad news: Furnace ran for about an hour (room temp was about 50; set point was 68 -- room temp never got close), and then shut off (despite the tstat calling for heat).

MaxMercy

If the tstat is calling for heat and you jump the terminals, does it restart? If so, I wonder if there isn't an intermittent break in the wiring between the tstat and the furnace controller.

Assuming it would restart if jumped, I think at this point I'd run a two wire and an old school Honeywell tstat into the living area and see if it stays running, and if so, will buy time until you can pin the problem down.

josephny

First thing I did was jump the terminals and the furnace did NOT come on.

Then, I wanted to jump the aux limit switch, but I don't see any exposed points at which I could do that.

So I removed the limit switch and found the sensor face covered in dirt. Gave it a quick finger wipe and the furnace came back on.

Could it be that the switch was simply dirty?

Do I need to clean inside where the switch lives? If so, how?

mattmia2

I would put one of these somewhere in the house in parallel with the ecobee to fire the furnace if the main t-stat fails to:
https://www.supplyhouse.com/ICM-Controls-SC060-SC060-Dryout-Thermostat-60F

MaxMercy

josephny said:

So I removed the limit switch and found the sensor face covered in dirt. Gave it a quick finger wipe and the furnace came back on.

Could it be that the switch was simply dirty?

The limit switch turns on the blower when the plenum reaches operating temperature (you don't want cold air blowing into the house). Dirt on the face of the switch might delay the start of the blower by a few seconds, but you said other than the pilot, there was nothing going on with the furnace - I assume the furnace plenum was cold because the burner wasn't running?

There are all sorts of sensors on modern furnaces to protect against thermal runaway or gas leakage. You could try poking at the wiring of the other sensors while it's running like your rollout switch (for instance) to see if you have a corroded terminal or something or even gently tapping the gas valve. I had one years ago that did this and it was an intermittent microswitch on the motorized flue damper.

josephny

Sorry, I meant to write that I removed the auxiliary limit switch and found it dirty.

Does this aux switch only control the blower? Just working off my very limited understanding, would I be correct to say that if the aux switch was dirty and preventing the blower motor from running, then the burner would come on and immediately rise to a high enough temperature to cause a shutdown (by some other safety device). Effectively, therefore, the aux switch failure could cause the entire furnace to stop working -- correct?

As for a roll out switch, I don't know where that is (or if the CMF80 has one).

I do like the idea of a backup tstat (run in parallel, with an unusually low setpoint (60)).

josephny

Almost a couple of hours later, the temperature reached the setpoint, furnace shut off, temp dropped below setpoint, furnace started up again.

The aux switch is still connected, but unmounted (physically removed) from the hole it was in.

mattmia2

Newer furnaces usually start the blower on a timer say 90 seconds after it fires the burner instead of on a thermostatic fan control. Need to see the schematic to know what the aux limit switch is but usually there is a second limit switch that is in series with the primary limit switch (which is part of a thermostatic fan control on older furnaces) to give it a second chance to shut down the burner if it overheats.

pecmsg

It sounds like the Limit was doing its job. When the furnace runs for about 15 minuets what's the temperature rise? Return and closest supply.

HVACNUT

josephny said:

Almost a couple of hours later, the temperature reached the setpoint, furnace shut off, temp dropped below setpoint, furnace started up again. The aux switch is still connected, but unmounted (physically removed) from the hole it was in.

Agree with @pecmsg. The circuit seems to be opening on high limit when it's in the proper location. 

This furnace has no return duct, correct? The air filter is in the door? Is there an air filter? Is it clean?

You cannot continue to run the furnace with the limit removed. It's a safety and it's doing exactly what it was designed to do. 

At this point you should have a pro check it. Could be airflow. Could be too high manifold pressure at the gas valve. Could be partially blocked flue. Is there air conditioning? Clogged evaporator coil?
Stay safe.

josephny

I believe this is the unit I have:

mattmia2

Oh, it is a gas power burner. That give it all sorts of extra reasons it might not be firing. The blower won't run unless it is hot because it is on a thermostatic fan control. The burner won't run unless both limits are below their setpoint.

josephny

Am I correct that the switches I have circled in like-colors are the same (i.e., the switches in the 2 red circles are the same device and the switches in the 2 blue circles are the same device)?

And, the switch in the blue circle is the one with the rotating dial with settable temperature levels for on, off and max-limit (with the round rod that can be pulled out or pushed in and for auto or manual fan operation).

josephny

Does this look like a properly functioning burner:

josephny

HVACNUT said:

josephny said:

Almost a couple of hours later, the temperature reached the setpoint, furnace shut off, temp dropped below setpoint, furnace started up again.

The aux switch is still connected, but unmounted (physically removed) from the hole it was in.

Agree with @pecmsg. The circuit seems to be opening on high limit when it's in the proper location. 

This furnace has no return duct, correct? The air filter is in the door? Is there an air filter? Is it clean?

You cannot continue to run the furnace with the limit removed. It's a safety and it's doing exactly what it was designed to do. 

At this point you should have a pro check it. Could be airflow. Could be too high manifold pressure at the gas valve. Could be partially blocked flue. Is there air conditioning? Clogged evaporator coil?
Stay safe.




Well, after running for about 15 minutes (with the aux limit switch removed), the furnace turned off. So, we know the reason it is shutting off is not because of the (now disconnected) aux limit switch.

No return duct -- air filter in door; no problem getting air.

No AC.

Could the fan and limit switch (the rotating dial switch) be the cause?

Is there any other safety/electrical device that would cause it to shut down?

SuperTech

It could be a burner control, a fan/limit control or maybe the centrifugal switch in the burner motor. Why don't you do the right thing for your tenants and get a professional on site at this point? It's kinda cold out there to be DIYing and firing the parts cannon at it.

mattmia2

if the limit switch shut off when it was mounted in its correct position it is overheating and someone needs to figure out why. it is not safe to disconnect the limit.

circles switches are the same.

a competent burner tech with the correct instruments is the only person that can say if it is burning properly.

josephny

SuperTech said:

It could be a burner control, a fan/limit control or maybe the centrifugal switch in the burner motor. Why don't you do the right thing for your tenants and get a professional on site at this point? It's kinda cold out there to be DIYing and firing the parts cannon at it.

Wow, you've create a whole story that is interesting, but not correct.

There are no tenants involved. And I'm not firing a parts canon.

I very much enjoy learning and DIYing, about a truly great many different things.

I'm grateful for your help, and I understand your comments come from a good place and with a concern for safety.

HVACNUT

josephny said:Is there any other safety/electrical device that would cause it to shut down?

Yeah. A lot of things. But on advice from counsel, I have to refrain from answering further questions. Nobody's blowing up on my account. 

josephny

I reached out to my long-time boiler tech and he says he does not work on these types of furnaces.

I reached out to my supply house for a recommendation and they said I should contact my gas company.

My gas company (Amerigas) is 100% incompetent at everything they do.

So, what am I left to do except call random people found via google and hope to find someone who is truly competent?

I suspect for you experts, the idea of a homeowner finding an expert is not particularly difficult. I can tell you from many years of experience, it can be very very difficult.

Jamie Hall

We have given you, the homeowner -- which all of us are, too, by the way -- the best advice over the internet we can. Which is to find someone who is competent and able to diagnose a very hazardous problem. We can't do it from afar, but only make some suggestions.

I agree that finding a competent person can be difficult, particularly with older or more unusual equipment. I would also suggest that Dr. Google may not be that person.

SuperTech

josephny said:

I reached out to my long-time boiler tech and he says he does not work on these types of furnaces. I reached out to my supply house for a recommendation and they said I should contact my gas company. My gas company (Amerigas) is 100% incompetent at everything they do. So, what am I left to do except call random people found via google and hope to find someone who is truly competent? I suspect for you experts, the idea of a homeowner finding an expert is not particularly difficult. I can tell you from many years of experience, it can be very very difficult.

I understand where you are coming from and I appreciate your effort to tackle it yourself. Sometimes what is difficult to take care of yourself even with the advice of the knowledgeable people on here can be fairly simple for a tech who is on site with the proper tools. It's not a complex furnace, you should have several hvac techs in your area familiar with it.

pecmsg

josephny said:

SuperTech said:

It could be a burner control, a fan/limit control or maybe the centrifugal switch in the burner motor. Why don't you do the right thing for your tenants and get a professional on site at this point? It's kinda cold out there to be DIYing and firing the parts cannon at it.

Wow, you've create a whole story that is interesting, but not correct.

There are no tenants involved. And I'm not firing a parts canon.

I very much enjoy learning and DIYing, about a truly great many different things.

I'm grateful for your help, and I understand your comments come from a good place and with a concern for safety.

Bypassing a Safety is unacceptable. It is NOT a troubleshooting tool.

Where are you that there are no techs capable to work on this unit?

dko

GL

pecmsg

pecmsg said:

josephny said:

SuperTech said:

It could be a burner control, a fan/limit control or maybe the centrifugal switch in the burner motor. Why don't you do the right thing for your tenants and get a professional on site at this point? It's kinda cold out there to be DIYing and firing the parts cannon at it.

Wow, you've create a whole story that is interesting, but not correct.

There are no tenants involved. And I'm not firing a parts canon.

I very much enjoy learning and DIYing, about a truly great many different things.

I'm grateful for your help, and I understand your comments come from a good place and with a concern for safety.

Bypassing a Safety is unacceptable. It is NOT a troubleshooting tool.

Where are you that there are no techs capable to work on this unit?

https://youtu.be/oRWC4IuwDr4?t=2

mattmia2

Doesn't the boiler tech know who is good?

josephny

So, no one knows anyone who knows this type of furnace.  

And the gas company can’t give me a date and time to get a tech out. 

So yesterday I went to a huge hvac supply place and bought a new pilot assembly, aluminum tubing, aux switch, peizo igniter wire.  Installed and the furnace ran great until 3:45am.   During what looked like a normal off state of the cycle, it just didn’t come back on.  

Would anyone be so kind as to take a look and let me know what I can try next while waiting to get a pro in?

it looks like the approx 550 watts being drawn when the furnace is running is either the blower motor or the burner motor or both.  After the last successful cycle, it was not drawing those 550 watts.  Not sure if that’s a clue. 

Jamie Hall

The bottom trace is power consumption? Staring you in the face. Looks like a motor is jammed or its start capacitor is toast. Question is, which one?