Community Forums

Johnynorthla · 09-07-2022, 08:15 PM

Trying to be proactive, I checked my furnace. To my delight it ignites, however, the burner keeps cycling, but each time the burner stays on longer and longer. It does work and produces heat. I have a dog, so I’m guessing dog hair, lint etc. may be clogging up the sail switch. So I ordered a sail switch and a high limit thermostats switch also.

Has anybody else had an issue such as this? Would love some input before I start taking it apart.

Skip426 · 09-07-2022, 11:56 PM

If the furnace hasn't been out for cleaning the whole squirrel cage is probably clogged with dust and hair .

Sail switch is operating , or furnace would not ignite.
Reduced air flow will overheat the combustion chamber causing the shut down ( high temp sensor ).
Full furnace clean out is on my two year maintenance list.

What brand of furnace do you have ?
Do you have the manual ?
Take pictures as you go , and have an old egg carton handy to keep screws sorted ; my furnace has about seven different sizes .

K7JV · 09-08-2022, 06:42 AM

The furnace on our 2021 Entegra Esteem does the same thing. It typically might take three to five ignition cycles before it finally continues burning. It is a nearly new furnace and doesn't have a lot of hours on it. I "watch" it, but I guess I'm not as concerned about it as I was. My guess is that the flame sensing thermocouple may not be in quite the right position and may not be reliably sensing flame. Note that this is a "new" furnace that was installed by the dealer last summer, as the original quickly developed a very noise circulation fan. They replaced the original rather than trying to correct the problem, as it was under warranty.

A typical start sequence might be for the fan to come on for maybe 10 seconds, the valve to open and the ignitor to start firing, and then after a couple of seconds the we hear the flame ignite and the ignitor stops firing. A "successful" start!

But, after maybe five to ten seconds, we hear the flame stop. After maybe five seconds or so, the sequence above begins again until it once again sees a "successful" start.

After maybe ten seconds or more, we hear the flame stop, again. The cycle repeats, perhaps several times. Each time, the length of time that the furnace is burning and operating correctly gets longer until after four or five re-lights, it stays on and operates properly for the rest of the period.

This scenario plays out virtually every time that the thermostat starts calling for heat after the furnace has pretty much cooled down, or hasn't yet run for a while. Once it has been used for a bit and has pretty much heat-soaked the unit, it just operates as it is designed to operate, cycle after cycle. I know it isn't right, but I also don't think there is a component problem that I think we need to worry about.

Persistent · 09-08-2022, 11:53 AM

So it works to keep you warm, but it is not good in the long run. Excessive burner starts will limit life of certain components. It is not urgent, but should be addressed when possible.

Flame sensing design could be bad
Position of the spark/flame sensor not correct (most likely)
Spark/flame sensor not working properly with the circuit board
Over temperature sensor is tripping. (Symptoms indicate this is less likely.)

Sail switch enables spark and opening of gas valve -- OK
Spark electrode also provides proof of flame -- Not OK
Time limit to prove flame expires and gas valve is closed
Cycle starts over
Eventually surrounding materials heat up enough to help prove flame

wolfe10 · 09-08-2022, 12:04 PM

Also, verify that there are no obstructions in the interior air flow-- either on the intake side or a crushed duct or closed vent.

Reduced air flow can contribute to high temp cut-out.

Johnynorthla · 09-09-2022, 06:30 AM

What brand of furnace do you have ?
Do you have the manual ?
Take pictures as you go , and have an old egg carton handy to keep screws sorted ; my furnace has about seven different sizes .[/QUOTE]

Dometic DFMD30111

It looks like I can open the hatch on the outside to access it, I can also access it from the inside but I’m guessing the fan motor & squirrel cage are facing outside when I compare it to internet/YouTube searches I’ve done. Once I gain access, how much disassembly do I have to do to access the Squirrel cage to clean it out?

My RV is in storage and I’m not able to get access easily, the place is locked down, owned by a local guy that I set appointments up with to gain access. So it might be a few days until I get back to this excellent resource of help!

Thanks everyone!

Johnynorthla · 09-09-2022, 06:41 AM

[QUOTE=K7JV;6301591]The furnace on our 2021 Entegra Esteem does the same thing. It typically might take three to five ignition cycles before it finally continues burning. It is a nearly new furnace and doesn't have a lot of hours on it. I "watch" it, but I guess I'm not as concerned about it as I was. My guess is that the flame sensing thermocouple may not be in quite the right position and may not be reliably sensing flame. Note that this is a "new" furnace that was installed by the dealer last summer, as the original quickly developed a very noise circulation fan. They replaced the original rather than trying to correct the problem, as it was under warranty.

Thanks, I’ll take a look but my experience with thermo-couplings is on house furnaces and hot water heaters, and I’ve found they usually just go bad. But I’ll check, you never know with these rigs!

It doesn’t surprise me that your dealer would rather just replace the unit rather then taking the time to troubleshoot and repair the issue! That seems to be the norm these days! When I was a young auto mechanic in the 70’s-80’s, we would rebuild just about everything, even wheel cylinders on drum brakes!

Johnynorthla · 09-09-2022, 06:53 AM

Quote:

Originally Posted by wolfe10

Also, verify that there are no obstructions in the interior air flow-- either on the intake side or a crushed duct or closed vent.

Reduced air flow can contribute to high temp cut-out.

Will do, but nothing has changed and wouldn’t that stop it from operating all the time? My unit ignites and cycles at first start up and stays on longer and longer with each cycle then eventually runs fine.

I’m hoping it’s just needs a cleaning, I’m guilty of not doing it since I’ve owned it from 2018! We winter camp once a year, and depending on temps, we sometimes only use our electric space heater, I can’t stand the noise and cycling of the furnace and the moisture it creates!

My 2nd RV had the truma combi system, was way better then these furnaces! And I loved the LP or electric option!

yeloduster · 09-09-2022, 02:18 PM

Quote:

Originally Posted by Johnynorthla

W I can’t stand the noise and cycling of the furnace and the moisture it creates!

If your furnace is installed properly it will not introduce moisture into the interior of your motorhome! If you are getting moisture it is coming from another source or your furnace or its installation is defective and DANGEROUS! If you are getting moisture from the furnace you are also getting carbon dioxide from the furnace!

Moisture can only come from the exhaust of the combustion chamber and that is directed to the outside.

I would make certain the furnace heat exchanger and exhaust is in good condition and installed properly. Do not run the furnace until you are confident that the combustion chamber, heat exchanger and flue are sound and properly installed!

Johnynorthla · 09-10-2022, 07:26 AM

Quote:

Originally Posted by yeloduster

If your furnace is installed properly it will not introduce moisture into the interior of your motorhome! If you are getting moisture it is coming from another source or your furnace or its installation is defective and DANGEROUS! If you are getting moisture from the furnace you are also getting carbon dioxide from the furnace!

Moisture can only come from the exhaust of the combustion chamber and that is directed to the outside.

I would make certain the furnace heat exchanger and exhaust is in good condition and installed properly. Do not run the furnace until you are confident that the combustion chamber, heat exchanger and flue are sound and properly installed!

It was always my understanding that these LP furnaces always produce moisture. I’ve had 3 RV’s and 2 of them had the same type of Dometic furnace, they both produced moisture. I’ve read others on this and other forums stated the same. I also have an explosive gas detector along with a CO2 detector, wouldn’t these detect the presence of any CO or LP?

yeloduster · 09-10-2022, 11:57 AM

Unvented heaters do add moisture. Stand alone catalytic heaters, wall mounted unvented catalytic heaters, the propane burners and the oven of your stove all have H2O as a byproduct of combustion that is introduced into the RV interior. Any cooking creates steam (water) into the air. People also exhale and sweat. This also adds moisture to the RV air. These sources add up and can be significant.

RV outside walls are thin and poorly insulated as compared to a modern home. When it is cold outside moisture in the RV air tends to condense on the cool walls.

Your RV furnace draws outside air into the furnace and uses that air to burn the propane. The exhaust of the furnace is then vented to the outside of the RV. The combustion process of the furnace is isolated from the interior of the RV. In fact the furnace tends to dry the air in the interior of the RV, not moisturize it.

Click this LINK. It is important to read the complete article because it starts by detailing how UNVENTED heaters add moisture. It then explains how your furnace does not add moisture and talks about moisture sources within your RV.