Propane Duo Therm Heater Troubleshooting (Won’t Ignite)

Fixing those heater issues range from easy and quick to having to replace the old heater with a safer upgraded model. Sometimes people won’t work on the older heaters and you end up replacing the heater.

One reason Duo Therm furnace won’t ignite is that it has gotten very dirty. To fix this situation, you need to vacuum out the combustion chamber. Or you may need to clean the air filter so that the airflow can work without hindrance.

To learn more about this topic, just continue to read our article. It has the information you need to know about so your Duo Therm heater works like a charm. Having the right information will lead you to the right solution quicker than in any other situation.

Old Vintage Duo Therm Furnace Problems


One of the biggest problems you will run across will be the DIY fixes that previous owners made. One newer owner found an aluminum delivery pipe that had a hole. The previous owner simply closed the hole using silicone. It took a while and a lot of searching for good parts to fix that mess.

But one thing about older furnaces is that they had few parts to break or go bad. Some of those older models only had a gas valve, pilot, thermocouple, burner, and the actual body that could break on you. Fixing these was a matter of finding replacement parts.

Ignition would be another issue and sometimes a good cleaning took care of the problem. If it didn’t you may have to find a new igniter or gas valve. Mostly with Duo Therm, the problems were little but they added up. Some people did not want to deal with those little issues.

If you have an older Duo-Therm, your biggest problem is not going to be problems that arise but finding the right parts. Some owners did a lot of gerry rigging to overcome those challenges.

Troubleshooting a Duo Therm Heater

When you have trouble igniting the pilot you may have to go into the control center which is behind the front grill. First, turn the thermostat to the off position. Then slide the grill off and slip your hand inside, the gas knob should be on the inside left edge.

Turn that gas control to the off position and wait 10 minutes. Turn it back on and reset your thermostat. This should restart the internal gas flow. Another issue that is simple to fix would be to look at your air intake valve.

If it is clogged, your furnace will not draw in enough air to the combustion chamber. To fix this issue, just clean the intake valve with a rag or vacuum cleaner.

Duo Therm Furnace Won't Ignite


Whether you have an old or a more up-to-date Duo Therm furnace, the ignition problems are the same. One of the first places you need to look at will be the propane tank. Not only to see if there is still propane in the tank but also to see if the gas is flowing properly.

In the latter case, you may need to change the regulator or valve. For the former problem, you will need to switch tanks or get them refilled. while you are checking the valve, check the line to make sure there are no kinks.

If those items aren’t the problem, you should check the pilot light and thermocouple to see if they have worn out. If so, changing them is your only repair. Next on the list will be your thermostat. If it has become or is faulty, then your furnace won’t light.

But these are not the only simple paces to check. When all of those locations are fine, you need to turn your attention to the intake airflow valve. This valve helps bring oxygen to your furnace plus distributes the heat around your room.

Cleaning is the best solution in this case. Finally, you may be experiencing some minor electrical problems. Frayed wires, loose connections so when all else fails, you need to follow the wires and double-check to see if they are okay.

Duo Therm Furnace Won't Stay Lit

One of the first places to look when this happens is your thermocouple. If the pilot light stays lit, but the flame shuts down when you turn the heater to on, then you have a thermocouple problem.

The fix for this issue is to replace the thermocouple. But that is not the end of the problem. If you replaced the thermocouple and the problem continues then you may be pressing the dial-in for a lot longer than you need to.

Once the thermocouple is heated, you should let go of the inward pressure and turn the dial to on. If that does not solve the problem, then something may have gotten between the regulator and the thermocouple.

It could be anything, even Teflon tape that has somehow found its way between the two parts. When that happens your fuel flow is hampered. Now if all of those items are fine, then it may be the regulator.

You can fix that by blowing some compressed air through it. If the compressed air does not open up the fuel flow then the regulator is bad and you will need to replace that part.

Or you can hire a professional to do all the checking to make sure all your parts are in good working order.

Duo Therm Furnace Fan Not Working


While the Duo Therm furnaces were good heaters, the biggest problem you will have is finding parts for them. Also, if it is the last model that the company made, the parts are very expensive and that was 17 years ago. Who knows how much they will cost today.

You can try to see if the fan switch is bad and if it is, you just have to replace it with something similar. That is the easy source. The bad source is that the fan motor may be blown and you may have a lot of trouble finding a replacement motor.

It has been almost 20 years since Duo Therm stopped making furnaces so finding replacement motors or parts may not be so easy. The experts say that you should replace the Duo Therm furnace with either one of the Suburban NT series or the Atwood/Hydroflame 8500 series.

The replacement may be costly initially but the new furnace may last you for a very long time before it needs any repair work done. Or you can spend a lot of time and money looking for replacement parts or motor only to have to do it again in a year or two.

It will be your choice of course, but the former option seems to be the better way to go.

Finding a Duo Therm Heater Manual

While finding parts for your furnace may be difficult and costly, finding a manual is not going to be the same experience. There are a lot of websites advertising that they have manuals for your Duo Therm furnace.

The first place to look would be the website at this link. it says technical services, manuals, and installation user manual on the landing page. Next up would be this website and it is a 32 page PDF file that you can easily read.

A third choice would be this website. It has manuals for all things Duo Therm including air conditioners, heat pumps, and thermostats. If you need more than just the heater manual this website may have you covered.

If Duo Therm is still in business, you should contact them directly. They should have their manuals digitalized for easy downloading and for good customer service. Going directly to the horse’s mouth is the best way, most of the time, to get the needed information, parts, and manuals that you need.

Also, do a good and thorough internet search to see if we missed any more websites that can help you out. Duo therm is still a popular RV supplier so it makes sense to keep their manuals where their customers can reach them.

Duo Therm Furnace Model Numbers


These model numbers come from just after Dometic took over Duo Therm-- 620515, 620525, 620526, 630515 & 630516 and that was in about 2004 approx. These two model numbers are from an earlier Duo Therm heater, 65930-064 and 65925 And 65930. Both may be from the 80s. Finally, there is this model number- 66012-005.

Finding model numbers for the old Duo-Therm furnaces is a bit difficult as people only place their numbers on the different discussion forums. They do not place a list of those model numbers so everyone can find theirs quickly.

If you want to find spare parts, the parts are listed under their own individual model number and not the furnace’s. Then you may have to look under Dometic’s web pages to see if the company lists any Duo-Therm model numbers there.

Generally, the different web pages are asking for a model number and do not provide any lists of them. Since Dometic took over Duo therm, the listings may be harder to find and be placed under the Dometic name.

How To Turn On a Duo Therm Heater


This is supposed to be a simple furnace to turn on. To start one, make sure the gas knob behind the front grill is turned to the on position first. This will involve removing the grill and sticking your hand inside to see what position the knob is in. If it is in the off position, then you will need to turn it the other way.

Once that is done, replace the grill and go to the ignition knob. You should have to press that knob in and turn it to start. Once the pilot light is lit, you release the pressure and turn the knob to on.

Sometimes people keep the inward pressure on the ignition knob for too long and the pilot light fails to ignite. It is all a matter of timing as you need to release it at the right moment. Once you release it and turn the knob to the on position, you should be fine. Don’t forget to set the thermostat to the heat level you need or want.

Checklist Of Parts To Double-check

When your heater fails to light, it pays to have a checklist handy so you can get to the source of the problem a lot quicker. This will save you time and help you not rely on your memory. Sometimes memory gets it wrong.

1. Check the fuel situation- this will involve propane in the tank, the regulator, and the fuel lines. You do not want any empty tanks, kinks in the line, or dirty regulators.

2. Check the ignition system- make sure it is in good running order and it is clean

3. Check electrical parts- here you are looking for broken, loose wires or bad connections, frays, and so on. Next, check your battery and its terminals. There may be corrosion on the terminals or the battery power is low.

Next, check the pilot switch, the sail switch, and the thermostat, as well as its batteries. make sure all are in good working order. Finally, check the blower switch and motor to make sure they have not worn out on you.

Some Final Words

RV furnaces seem to be almost the same no matter who makes them. they are simple devices that usually have few parts that can go bad on you. Fixing the problem is not hard unless you have a vintage furnace that no one makes parts for anymore.

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