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Ask Dave: RV furnace has low airflow and isn’t hot. Why?

Dear Dave,
The RV furnace has always worked well, but this last week it seems it isn’t heating the interior as quickly as it did a few months ago. I checked the vents and nothing is blocking them. The air blowing is warm but used to be much warmer. And while the heat is on, I can’t light the stove burners; I have to turn the furnace off, and then the stove will light. That has never happened before, so I think the two may be related. —Cheryl, 2016 Coachmen Leprechaun 220QB

Dear Cheryl,
You might have a couple of issues going on here. I would start by verifying there is 12-volt power to the RV furnace. I know I sound like a scratched record; however, low voltage is the culprit the majority of times in these situations. First, does this happen when you are connected to shoreline power or dry camping? If you are connected to shoreline power, the converter should be putting at least 13.2 volts into the furnace and 13.6 volts if the batteries are no good.

Verify voltage

Get a multimeter and verify what voltage you have at the batteries.

The next thing I would do is verify what voltage is at the module board at the furnace. Doing this means taking some of the housing apart from the backside. It may not be something you are comfortable with.

If you are getting low voltage, then there is something wrong with your wiring. I would then take the unit out and bench-test it with a good 12-volt source and open venting. This would verify that the motor is running fast enough to lift the sail switch and that there is good airflow coming from the return air intake and going out over the burner assembly. It would also verify good airflow coming from the outside air intake and going out the other air exchange, and that the unit is lighting and the burner assembly is good. You can take a look at the outside vents to make sure they are not clogged. Then look inside and make sure none of the supply hoses is kinked or disconnected.

I have seen situations where the main supply hose coming off the RV furnace has slipped off and warm air is blown into the basement and not to the vents. This could be one reason you are getting lower airflow and temps.

Could be a weak regulator

Another issue could be a weak regulator, especially since you need to shut the furnace down to light the stovetop burner. Since you have a Class C, your unit has an ASME tank with a regulator on the tank. Typically, a technician would check the regulator using a water column tester at the furnace or other appliance. It should read 11” of water column. You can do a manual test by turning on one of the burners at the stovetop and then slowly turning on another. Watch to see how the flame reacts—it should be a steady blue. If it is jumping around, orange, or goes down and does not come back up, then the regulator is not getting enough pressure through it. I would recommend getting a technician to test it professionally and change it, as well.


 You might also enjoy this from Dave 

RV ‘Gremlins’, Part 5: Forced air furnaces and why they’re so finicky

I typically don’t get as many questions about furnace efficiency as other appliances, mostly because of how people are using their units and how often the furnace actually gets used.

Most RVers store their rigs in the winter, so the furnace only gets used slightly when the temperature dips in the mountains or during autumn, so it doesn’t get tested as much in extreme conditions.

Continue reading


Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

Read more from Dave here

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Bob
1 month ago

From the symptoms before going through all the voltage tests, gas pressure would be the first thing to test. The fact that the furnace has to be turned off before the stove will light points to a low gas flow. The furnace requires much more propane than the stove burners.
Since the furnace is coming on, that just about eliminates a low voltage problem, since the fan is blowing enough air to close the sail switch.

Thomas D
3 months ago

Having 2nd thoughts about this problem
It sure would be nice to know what fixed the problem
Maybe the original poster could come back, refer to original post and tell us what WAS wrong and what the fix was?

Cee
3 months ago
Reply to  Thomas D

Thomas D, I arrived home yesterday & started looking into Dave’s suggestions. My 2 12v house batteries are at 12.8 so I can rule that out & I haven’t found any kinks in the supply hoses… yet. So I have no fix yet. You brought up the possibility of not enough propane which initially crossed my mind but I trusted the gauge on my on-board tank & went on the premise that you either have propane or you don’t, it’s not like a battery that will run down. Tomorrow I will drive my motor-home to town & top off the propane tank and try to recreate the 2 issues. Dave and Bob P suggested I have the regulator tested; hoping my propane shop can do that or I’ll have to wait a few months for an appointment with the RV center; ugh! Bill Bateman had a good point about the stove top flame vs removing the furnace. I replaced the sail switch last year but that is basic compared to pulling the furnace. If I go forward with that I see a lot of YouTube videos in my future.

Thomas D
3 months ago

Simply? Is there enough propane? very first thing I’d check!
The little gauge on the tank may be way off.

Bob p
3 months ago

The regulator would be the first place I would check since his description indicated having to turn the furnace off to light the stove, that’s a dead giveaway to low pressure. Are you letting Johnny Robot answer the questions?

David Solberg
3 months ago
Reply to  Bob p

I agree, however the average RV owner can not test the regulator without a water column tester and the expertise to use it so I thought it was important to verify everything she could do before spending the money at a service center for something that she could fix.
And no Johnny Robot!

bill bateman
3 months ago
Reply to  David Solberg

But still .. Checking the color and activity of the flame on the stovetop is MUCH easier then removing the furnace. Also more likely since the stove and furnace are sharing symptoms.

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