Grand Design furnace short cycling problem

[velran]

What color is the flame?

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

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In the furnace the flame at the base is blue but turns to orange everywhere else on the burner surface. Flame is blue in the gas stove, the water heater, and fridge. Yes, I did bypass the thermostat when bench testing it (just in case I also replaced the thermostat prior to that).

[JustUs&doggo]

In the furnace the flame at the base is blue but turns to orange everywhere else on the burner surface. Flame is blue in the gas stove, the water heater, and fridge. Yes, I did bypass the thermostat when bench testing it (just in case I also replaced the thermostat prior to that).

Ok....that actually sounds like you have a low flame....look for kinked lines....maybe the propane is not forceful enough to fully exhaust the tube? I'm grasping at straws here now


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[velran]

Ok....that actually sounds like you have a low flame....look for kinked lines....maybe the propane is not forceful enough to fully exhaust the tube? I'm grasping at straws here now


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Can a low flame cause the furnace to overheat?

[JustUs&doggo]

I think low pressure would...wont force the exhaust gas out fully....but i am not sure. My first thought would be that it would build up soot which would retain heat....

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[velran]

I think low pressure would...wont force the exhaust gas out fully....but i am not sure. My first thought would be that it would build up soot which would retain heat....

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The only thing that hasn't been replaced is the gas line between the furnace to the first junction where it splits into three (furnace, water heater, main line). AirExcel and Grand Design are out of ideas and at this point concluded that this is normal. I don't think it is and I'm looking for Imagine 23BHE/21BHE owners who I could share with me how their furnace runs.

[openrangeowners]

Can you hook the furnace up to another gas line (obviously after the regulator) to test it. Actually I would replace the regulator first and see if the problem still exists, then replace the gas line to the furnace. This should not cost very much to do.

The gas line may have in internal restriction or the regulator may be faulty - can you check the gas pressure with a manometer?

https://www.amazon.com/Manometer-RIS...0811937&sr=8-3

[Skiddy]

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?

If I understand correctly, you bench tested the unit(s) with the same short cycle result. Bench 12V, bench propane and bench thermostat or equivalent call for heat. If all this is true, why would the operation be any different in the rig? You know the power is good regardless of what the rig power is like and you know the propane supply is good regardless of any rig issues (good to know all other rig propane appliances working well) and you know the rig thermostat is good as it, like the power and propane supply, was not part of the bench test.

Although not what you or the service techs were expecting perhaps the units are now designed to operate this way. The only other consideration is the batch of units all have the same faulty part from the factory, hence your replacement operated same as the original.

[velran]

Can you hook the furnace up to another gas line (obviously after the regulator) to test it. Actually I would replace the regulator first and see if the problem still exists, then replace the gas line to the furnace. This should not cost very much to do.

The gas line may have in internal restriction or the regulator may be faulty - can you check the gas pressure with a manometer?

https://www.amazon.com/Manometer-RIS...0811937&sr=8-3

I think this is a great idea! I will do that and report back. We check the gas presure and it reads 11 WC.

[openrangeowners]

Is 11 WC static or when the furnace is operating? Still could be a restriction somewhere that allows full pressure when static, but reduces when drawing a large quantity of LP.

[velran]

If I understand correctly, you bench tested the unit(s) with the same short cycle result. Bench 12V, bench propane and bench thermostat or equivalent call for heat. If all this is true, why would the operation be any different in the rig? You know the power is good regardless of what the rig power is like and you know the propane supply is good regardless of any rig issues (good to know all other rig propane appliances working well) and you know the rig thermostat is good as it, like the power and propane supply, was not part of the bench test.

Although not what you or the service techs were expecting perhaps the units are now designed to operate this way. The only other consideration is the batch of units all have the same faulty part from the factory, hence your replacement operated same as the original.

Very interesting about the same problem due to the same batch. However, mine was 2516 and the one I received is 2516A so I would guess it is a different batch.
The bench test intended to eliminate airflow restriction occurring in the ductwork which is the most common reason for overheating. We also bypassed the thermostat.