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Can you help me with a dometic furnace that won’t light? Its…

Customer Question
Hi can you help...

Hi can you help me with a dometic furnace that won’t light?

Mechanic's Assistant: Just to clarify, what are the exact lights you're talking about?

Its a dometic furnace dfmd 25121 that won’t light fan comes on but furnace won’t light

Mechanic's Assistant: What is the make/model/year of your RV?

Coachman freedom express 2019 292bhds

Mechanic's Assistant: Are you fixing your Express yourself? What have you tried so far?

I’d tried turning the thermostat off and on several times made sure I have propane reset the furnace on the switch on the furnace

Mechanic's Assistant: Anything else you want the Mechanic to know before I connect you?

That’s probably good

Submitted: 1 year ago.Category: RV
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Answered in 23 minutes by:
11/8/2020
RV Mechanic: Chris (aka-Moose), RV Mechanic replied 1 year ago
Chris (aka-Moose)
Chris (aka-Moose), RV Mechanic
Category: RV
Satisfied Customers: 77,620
Experience: 24 years of experience diagnosing & repairing
Verified

Welcome to Just Answer I'm Chris aka Moose, I'm sorry you are having problems with your RV. I will do my best to help you get this resolved. If I happen to be helping another or step away during our communication, please know I will follow up as soon as I am back available/online. I try to be online for about 10+ hours a day, midday and late-night shift.

  • Have an assistant turn the furnace on while you are outside the camper at the air intake/exhaust, do you smell propane there and can you hear a clicking noise?
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Customer reply replied 1 year ago
No clicking and no smell of propaneThanks for your help by the wayI have propane and can run my hot water heater and stove top
RV Mechanic: Chris (aka-Moose), RV Mechanic replied 1 year ago

When was the last time the furnace worked?

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Customer reply replied 1 year ago
About a week agoWe had a major rain storm today, not sure if that did anythingIt's about 38 outside and we are a bit cold ��
RV Mechanic: Chris (aka-Moose), RV Mechanic replied 1 year ago

Do you have a voltmeter so we can do some testing on the furnace sensors to see why it is not opening the gas valve and why ist not turning on the igniter?

In the meantime, turn on your stovetop to get some heat going so you do not get cold. If you have a baking sheet, put that on the stovetop to get a larger heating displacement surface.

Do you have an electric heating fireplace below the TV you can turn on?

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Customer reply replied 1 year ago
I don't have a voltmeterWe are running the electric heaterAny other way to test that without a voltmeter?
RV Mechanic: Chris (aka-Moose), RV Mechanic replied 1 year ago

Unfortunately, there is no other way to test without a voltmeter.

I believe the sail switch is the issue. It moves when the blower comes on, and tells the circuit board the blower is going, so turn on the gas and igniter. https://pantherrvproducts.com/dometic-atwood-33082-furnace-sail-switch-with-bracket-upgrade-kit/

Here are some diagrams to see the wiring diagram and parts inside https://www.dometic.com/assets/55/72/33400_55572.pdf

You can watch the sail switch and see if it's moving fully once the blower comes on as well as assist it to move all the way or briefly bypass it with a paper clip to see if that's the issue.

Thank you for visiting Just Answer, I hope I was able to answer your question. If you need to follow up on this concern please use the reply button. If you like my answer please reply so I can mark your question complete. Moose

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Customer reply replied 1 year ago
Ok thanks!
RV Mechanic: Chris (aka-Moose), RV Mechanic replied 1 year ago

Glad to help

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Chris (aka-Moose)
Chris (aka-Moose), RV Mechanic
Category: RV
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