Furnace Short Cycling Burn

[ROC-REQS]

Maybe someone here can give me some ideas of what may be happening and/or suggestions on how to troubleshoot the problem.

The problem I'm experiencing is a very short furnace burn cycle (in the order of 15 - 30 seconds) after the inside temperature reaches the thermostat setting.

We have a 2015 361REQS Eagle Premier 5vr with an Atwood Excalibur 8900 III Series 40,000 BTU Hydro Flame Gas Furnace (Model # 8940) and a Coleman/Mach Single Stage Heat/Cool Digital Wall Thermostat.
We were plugged into 50A shore power with full LP tanks.

The furnace brought the inside temp to setting (71 degrees) with no problem.
Here's what happened after the inside temp became stable at 71 Deg.

1. Thermostat dropped to 70 Deg.
2. Furnace blower came on for the normal duration prior to furnace igniting.
3. Furnace ignited.
4. Thermostat increased to 72 Deg. within seconds (~15 - 30 seconds)
5. Furnace flame / burner shut off.
6. Furnace blower continued for normal duration.

It then took a few minutes (e.g., 10 - 15min) for the thermostat to drop to 70 Deg. and the cycle repeated.

Outside temps were in the 40s.

I've already had the thermostat replaced once.
I've also put insulation inside the wall around where the thermostat is mounted to the wall.

Any ideas or thoughts on what may be happening here and/or the cause for the furnace's short burn cycle?

Thanks in advance for any suggestions and/or ideas.

[mike837go]

According to your description, I'd say the thermostat is at fault. If it believes the room temperature has dropped, it is calling for heat. The furnace is doing it's best to respond to the irrational input from the thermostat.


A common problem in houses is cold air in the wall behind the thermostat. It causes all kinds of overtemp/cycling issues.


My suggestion is to remove the thermostat from the wall and neatly cover the hole with duct tape. Then reinstall the thermostat. Also look for any potential drafts that could be confusing it.

[Ela1948]

I have something of the same issue. It IS the digital thermostat that is the issue. Unfortunately, I don't think it's faulty!! I replaced it because the old thermostat was not digital and it was forever coming on and going off. The trailer would cycle between warm and too cold with the old thermostat. As soon as your blower kicks on, it moves air and changes a very sensitive thermostat. I'm going to try Mike837go's suggestion with the duct tape but I'm not too optimistic. My thermostat hangs on an interior wall which I would think wouldn't be very cold. The sensitivity of the thermostat is the issue. An older analogue thermostat will fix your current problem but you probably will not like the temperature swings that come with that thermostat.

[mike837go]

Plus the whole technique of heating a building using hot air is quite prone to wide/erratic cycling issues. Ask me about my last house with the oversized hot air furnace...


Like Ela1984 says, a mechanical thermostat will dampen the cycling in favor of very wide swings in temperature.


Try getting rid of any drafts near the thermostat. Especially, make sure none of the registers blow in the general direction of the thermostat.

[us71na]

My Dometic digital thermostat has the ability to have a 1 degree or 2 degree temperature differential that can be made in the set up.

[campitout]

Could be a flame sensor/thermocouple if it has one. If it is dirty that will cause a furnace to recycle. It would be about the diameter of a pencil and a couple inches long and in direct contact with the flame. Steel wool to clean and that should take care of it.

[Fairenatic]

Originally Posted by mike837go

Plus the whole technique of heating a building using hot air is quite prone to wide/erratic cycling issues. Ask me about my last house with the oversized hot air furnace...


Like Ela1984 says, a mechanical thermostat will dampen the cycling in favor of very wide swings in temperature.


Try getting rid of any drafts near the thermostat. Especially, make sure none of the registers blow in the general direction of the thermostat.

Good advice. I have seen so many thermostats with gaping holes behind them with air rushing by the thermostat. Foam works well.

[ROC-REQS]

Thanks for the replies everyone.
As always, some good suggestions have been provided.

The trailer is put away in winter storage now. I plan to do some more troubleshooting in the spring.

We're hoping to take a trip to the Jayco factory this summer, if nothing is resolved before then, maybe I'll reach out to them for some help and advice.

I'll post any updates and if I ever find a resolution.

[CharlieD]

look up "heat anticipation" for your particular furnace

[ROC-REQS]

Originally Posted by CharlieD

look up "heat anticipation" for your particular furnace

Hi CharlieD,

Thanks for the suggestion.

I have a digital Coleman Mach Thermostat, which I don't believe has an adjustable heat anticipatory.

I do think it's a problem with the thermostat or the location of it.
Because once the furnace burn starts, the thermostat does a 2 degree increase within seconds and shuts down the furnace.

In the spring I plan to setup a room thermometer next to the thermostat to see if the room thermometer's temperature reading is consistent with the thermostat.
I'm hoping that will help start to isolate the cause.

Thanks again for your reply.

[ROC-REQS]

Just an update on our on-going effort to isolate the cause of our furnace short cycling problem.

Talked with a tech from Atwood the other day and he believes the furnace is the cause of what we are experiencing (not the thermostat).

We will be taking the trailer to our dealer mid-march for them to further investigate the issue and hopefully get it resolved.

After talking with Atwood and our dealership, I have confidence we'll get to the bottom of what's causing this issue and will have it resolved before this camping season starts.

I'll post once this issue is resolved with what turns out to be the cause and what the fix was.

[dalebra]

Thanks for keeping us up to date on a resolution.

[ROC-REQS]

Originally Posted by dalebra

Thanks for keeping us up to date on a resolution.

You're welcome.

Our back-up plan is if the dealership can't fix the problem is to see if we can't schedule an appointment with Jayco's service department.

We're hoping to do a trip this summer to tour the factory anyway.

Hopefully it doesn't come to that. Would rather relax touring the area and the Jayco factory when there then have the trailer in for warranty work.

[dalebra]

Originally Posted by ROC-REQS

You're welcome.

Our back-up plan is if the dealership can't fix the problem is to see if we can't schedule an appointment with Jayco's service department.

We're hoping to do a trip this summer to tour the factory anyway.

Hopefully it doesn't come to that. Would rather relax touring the area and the Jayco factory when there then have the trailer in for warranty work.

The issue you have can be diagnosed by any qualified HVAC technician. RV, residential or commercial, they all have the same operating principals.

I'm lucky as I have one in the family.

[Ali#1]

Originally Posted by ROC-REQS

Maybe someone here can give me some ideas of what may be happening and/or suggestions on how to troubleshoot the problem.

The problem I'm experiencing is a very short furnace burn cycle (in the order of 15 - 30 seconds) after the inside temperature reaches the thermostat setting.

We have a 2015 361REQS Eagle Premier 5vr with an Atwood Excalibur 8900 III Series 40,000 BTU Hydro Flame Gas Furnace (Model # 8940) and a Coleman/Mach Single Stage Heat/Cool Digital Wall Thermostat.
We were plugged into 50A shore power with full LP tanks.

The furnace brought the inside temp to setting (71 degrees) with no problem.
Here's what happened after the inside temp became stable at 71 Deg.

1. Thermostat dropped to 70 Deg.
2. Furnace blower came on for the normal duration prior to furnace igniting.
3. Furnace ignited.
4. Thermostat increased to 72 Deg. within seconds (~15 - 30 seconds)
5. Furnace flame / burner shut off.
6. Furnace blower continued for normal duration.

It then took a few minutes (e.g., 10 - 15min) for the thermostat to drop to 70 Deg. and the cycle repeated.

Outside temps were in the 40s.

I've already had the thermostat replaced once.
I've also put insulation inside the wall around where the thermostat is mounted to the wall.

Any ideas or thoughts on what may be happening here and/or the cause for the furnace's short burn cycle?

Thanks in advance for any suggestions and/or ideas.

Next time when it happens try hot wiring thermostat . The furnace should come on if the thermostat is at fault. If the furnace does not come on check the limit switch. You can also hot wire the limit switch. Most likely it is the limit switch.

[ROC-REQS]

Thought I would post an update on what's been going on with my furnace issue.

The trailer's been at the dealership for the past week while they've been running tests on the Furnace & T-Stat, under Atwood's guidance in an attempt to isolate the cause.

All tests run on both the T-Stat and Furnace showed both were operating properly and spot on.

Then, on Atwood's suggestion, the dealership ran the furnace for 6 hours with the T-Stat set to 74 Deg. and then after 6 hours took temperature readings at various locations around the trailer (i.e., using a heat sensor gun).

Background note: Our floor plan is such that the kitchen counter top shelf attaches to the wall very close to where the T-Stat is located on the wall. See picture below

The counter top temp near the T-Stat measured at 54 Deg.
And the wall between the counter top & T-Stat measured 61 Deg.

So, the thought is that the problem is being caused by the location of the T-Stat in relationship to the kitchen counter top.

The dealership currently has a call into Jayco to see what Jayco's response / recommendation / suggestion is to their finds.

I'll post an update when I hear what Jayco's response is and what the final resolution is.

It would be interesting to hear if any other owners of a similar floor plan (e.g., 361REQS EP/NP, 36REQS Pinnacle) are experiencing anything similar.

[dalebra]

If you assume the stat is good and the furnace is good then it's caused by location. Which could be a draft from either inside the wall or a draft of heat blowing on the stat from a register.
1. Where is the heat vent in the bathroom in relation to the stat?.
2. I can't tell what they are but could the 2 devices on the wall above the stat be generating heat? I can't tell what they are from the pic except that one is the tank gauge panel. are either of them warm?

[ROC-REQS]

Originally Posted by dalebra

If you assume the stat is good and the furnace is good then it's caused by location. Which could be a draft from either inside the wall or a draft of heat blowing on the stat from a register.
1. Where is the heat vent in the bathroom in relation to the stat?.
2. I can't tell what they are but could the 2 devices on the wall above the stat be generating heat? I can't tell what they are from the pic except that one is the tank gauge panel. are either of them warm?

Hi Delebra:

Thanks for the reply.

The Heat Vent in the Kitchen is location in front of the kitchen cabinet (see pic) so the cabinet is blocking the air flow to the T-Stat.

1. The Bathroom heat vent is away from the wall between the toilet and shower, its location is not in line with where the T-Stat is mounted - probably in-line with ~center of the kitchen wall looking at the picture (e.g., to the left of the wall outlet). But that's something I hadn't thought about.

2. The 2 devices on the wall is a switch (for ceiling fan) and control for fantastic fan roof vent and its a wall outlet to the left. Non-heat generating devices.

I've put insulation in the wall behind the T-Stat and have moved the T-Stat as far away from the counter top as possible.

Not sure what material Jayco used for the counter tops, but I was surprised its temp wasn't more the 54 Deg. after 6 hrs of running the furnace.

[dalebra]

Originally Posted by ROC-REQS

I was surprised its temp wasn't more the 54 Deg. after 6 hrs of running the furnace.

Yes indeed, I am surprised that the countertop was only 54 Deg. also.
You would think it would take longer than 15-30 seconds to make a 2 degree rise too.
It will be interesting what the results are. And I am surprised that Atwood was not more help.

Keep us posted.

[ROC-REQS]

Originally Posted by dalebra

... You would think it would take longer than 15-30 seconds to make a 2 degree rise too. ...

I did some self testing at home before taking the trailer into the dealership.
Had the T-Stat set for 70, let the furnace run for ~1.5 hrs, then started timing burn cycle times. All were ~1min in duration. Had a house thermometer sitting on the counter next to the T-Stat. When the T-Stat adjusted 2 Deg. the house thermometer adjusted ~0.2 deg. That's why I originally thought it was a T-Stat issue.

Originally Posted by dalebra

... It will be interesting what the results are. ...

I'm also very curious and anxious to hear what Jayco has to say. This issue has been on record with them since Sept. of 2014. Jayco sent me a new T-Stat then, because at that time they also thought it was a T-Stat issue.

Originally Posted by dalebra

... And I am surprised that Atwood was not more help. ...

IMO I think Atwood was very helpful in providing assistance and suggestions to the dealership to help isolate the cause.
When they confirmed the T-Stat and Furnace was working properly, I don't think it's realistic for Atwood to help in location adjustment, because they don't know the details of the floor plan. IMO that's really a Jayco issue/resolution.

Originally Posted by dalebra

Keep us posted.

Will do