Grand Design furnace short cycling problem

[velran]

Does anyone else with a Grand Design (we have the 23BHE) have a furnace short cycling problem?
The flame will go off every 4-5 minutes and the igniter ticking sound will start and this cycle will repeat. The furnace doesn't stary on for more than 5 minutes.

[JustUs&doggo]

That has been a recent trend with the thermal cutout fuse on the unit. It is a high temp limit that cuts propane until the heat chamber cools down. Usually this is caused by a bad/failing thermal cutout or a blockage in the tube. Usually it is from spider webs or dirt daubers.

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[openrangeowners]

Make sure all of your vents are open and unobstructed. Also make sure the ducting is not kinked behind cabinets, in the underbelly, etc. The high temperature cutoff switch is likely failing. The more it cycles the more likely it will cycle more often. It weakens every time it cycles.


Check out the most recent Changing Lanes YouTube video on winter camping. They talk about the sail switch failing (will also cause the furnace to short-cycle). Both are replaceable if you know how to remove your furnace to gain access. They carry spares.

[velran]

Hey everyone,

AirExcel sent us a new furnace and even then it kept happening. That eliminated being an issue with the furnace. Grand Design sent another mobile RV repair company for a second opinion. After almost three weeks of back and forth where everyone thinks and admits this is an issue, the tech and Grand Design decided that this is normal. They are saying that the furnace rests a couple of times until it reaches the desired thermostat temperature. Rests meaning that the furnace runs for about four minutes and then the flame goes off for about a minute. The hi-limit switch makes contact again, the igniter makes a ticking sound and the flame comes back ON (blower is ON the entire time). These stops of flame ON flame OFF will continue until the thermostat reaches the desired temperature.


I have multiple techs telling me that a furnace should continually run until the thermostat cuts it off.

Does anyone else with a Suburban SF 25Q furnace experience the same thing? We have Imagine 23BHE so if you have this model or 21BHE I would greatly appriciate if you let us know if your RV does the same thing.

[tfgd21bhe]

I have a 2020 21bhe with the Suburban SF25Q furnace and it does not short cycle

[JustUs&doggo]

I am willing to bet then, that it is inadequate air flow. If it were mine I would run the furnace with one duct line off at a time to see which line is kinked or blocked. If none do the trick and it short cycles with all ducts off the unit so it can breathe fully, you have either a propane regulator problem (doubtful) or a 12 volt problem. My money is on kinked or blocked duct runs in the underbelly.

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[velran]

We checked all ducts and even added another two 4" ducts and it still does the same thing. Then, we pulled the unit out and it did the same thing on a bench test. finally We received a new unit from AirExcel and....it does the same thing! What else could it be?

[JustUs&doggo]

I would start with 12v. If not enough juice is getting to the blower it will not move enough air. You can try using a fresh 12v battery on the bench tied in to the supply of the furnace. Please make sure it is fused if you do that. Next if that passes, would be getting the regulated propane supply pressure tested. It could be getting the wrong mixture but check and diagnose 12v first.

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[velran]

I would start with 12v. If not enough juice is getting to the blower it will not move enough air. You can try using a fresh 12v battery on the bench tied in to the supply of the furnace. Please make sure it is fused if you do that. Next if that passes, would be getting the regulated propane supply pressure tested. It could be getting the wrong mixture but check and diagnose 12v first.

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So the blower is getting 12.61V - I tested it while it was on the bench. Do you still think it could be a battery issue and worth getting a new one to test? Also, it's connected to the shore line the entire time. I do agree with your theory that it's getting the wrong mixture and therefore in my opinion causing a bigger flame in the combustion chamber. However, I replaced the gas regulator too. Still getting too hot and the flame goes off every 5 minutes.

[JustUs&doggo]

So the blower is getting 12.61V - I tested it while it was on the bench. Do you still think it could be a battery issue and worth getting a new one to test? Also, it's connected to the shore line the entire time. I do agree with your theory that it's getting the wrong mixture and therefore in my opinion causing a bigger flame in the combustion chamber. However, I replaced the gas regulator too. Still getting too hot and the flame goes off every 5 minutes.

What color is the flame?

Is there any way to take the thermostat out of the question just in case?

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