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The Ultimate Suburban RV Furnace Troubleshooting Guide

Keeping yourself warm in the cold of night or dead of winter is a top priority when you’re on the road in an RV. That, of course, is where your RV’s trusty furnace steps in. 

One of the largest manufacturers of RV furnaces is Suburban. They are usually trustworthy machines that will last you for quite a while. Ideally, you’d never run into any issues while you’re running your Suburban RV furnace.  Like everything in your RV, though, there is a slim chance that something might go afoul. 

This Suburban RV furnace troubleshooting guide will show you what to do in the event that your furnace is malfunctioning. A faulty gas valve is the usual culprit, but you could be looking at firty vents or electrical failures as well. 

Suburban RV Furnace Troubleshooting Guide 

Understanding how your Suburban furnace works will help you troubleshoot any potential issues. 

The type of furnaces made by Suburban installed in recreational vehicles are known as direct vent sealed combustion furnaces. Force draft furnaces use a sealed combustion chamber that gets vented to the exterior of your RV. From the outside, the furnace takes air and isolates it from the air within the room. 

A motor then drives an impeller wheel, drawing that intake of air into a combustion chamber. This process forces the gasses out through the furnace. Another impeller wheel circulates the ‘room air’ across the chamber where it is heated up. 

Finally, a blower forces hot air into your vehicle’s living area. This is done in different ways depending on your specific type of RV. It might work through a duct system, or through a frontal grille on the furnace cabinet itself. Models with this front grille are referred to as ‘direct discharge.’ 

From an electrical standpoint, your suburban furnace operates on a 12 volt current of DC power. That power is coming either from a battery or your RV’s converter. Most Suburban forced combustion furnaces are designed to be used with propane. 

As you can see, there are a lot of moving parts that make your Suburban RV furnace tick. All of those parts can run into their own unique problems. As you troubleshoot, keep the entire structure of the furnace in mind. Doing so will help you mindfully perform repairs. 

With the basic functions of the furnace in mind, here are some of the common problems these models can encounter. 

The Furnace Does Not Ignite

Across the board, no matter the brand or age of a furnace, failure to light is the most regularly encountered issue. 

In Suburban models, this is commonly an issue with the gas valve. Listening to it and smelling it as you try to turn it on can help clue you in. 

If you are trying to light your furnace and hear the characteristic thunk sound but don’t smell any gas, it’s time to check the gas valve. It can be tricky to get to the gas valve on Suburban furnaces when compared to other brands, such as Atwood. It’s worth checking, however, as the valve testing poorly means it will need to be replaced. 

 personally buy items that will last. So if you’re looking for a for a simple, reliable, and still very affordable devise, then the Fluke 101 digital multimeter is what I would recommend for most users. From years of home projects to RV projects this multi-meter has served me well and I still use it all the time.

Testing The Gas Valve 

Before you can test the gas valve, you’ll need to get to it. On a Suburban model, the way to do this is to remove the working parts of the furnace from its case. You should see the gas valve nestled between the blower wheels. Do not take the gas valve apart; doing so could be potentially dangerous. 

Use a multimeter set to ohms to run this test. You’ll want to connect the leads on your multimeter to the terminals of the solenoids on your gas valve. For continuity, you’ll be testing these one at a time. 

The value should be roughly between 30 and 50 ohms – it doesn’t need to be exact, but it should be in the ballpark. However, an extreme high or low is an indicator that something is afoot and the valve should be replaced. 

To remove it, use a ⅝ crowsfoot and a ⅜ ratchet with an extension part. 

The Furnace Blower Won’t Start 

Similar to the problem of the furnace failing to ignite, sometimes you might notice that the blower isn’t going as it should. There are a few things that might lead to a malfunctioning blower: 

      • The time delay relay has failed. A lot of Suburban models are of the time delay variety. That means that the relay has a big job ahead of it, and if it fails, you’ll notice right away. 

      • There isn’t enough power coming from the RV’s batter to the relay switch. You can check this with a multimeter. If the voltage is low, that might cause the current to spike and trigger the circuit breaker. Reset the breaker and try again 

      • Loose wiring. This isn’t terribly common, but it’s something that might be easily fixed. You may need to replace the wiring entirely if they’ve worn down enough to loosen their connections. 

      • The thermostat isn’t connected properly to the furnace. This is likely causing other problems besides just the blower not working. Try to strengthen the connective wirings. 

      • The motor that powers the blower is faulty. 

    The Furnace Runs For A Few Seconds, Then Stops 

    Another potential bug you might notice with your Suburban furnace is that it is not staying lit. You see it run for a second or two only for everything to fizzle out without clicking back on. 

    The main cause for that is a clogged exhaust or intake vent. With the air moving to and fro within it, it’s easy for debris and dirt to become caught in these vents. 

    All the vents need is a good cleaning, something you can do with a good wire brush. Wear goggles and gloves if you’re worried about the debris getting in your eyes or on your hands. Once you’ve cleaned it out carefully, try to ignite the furnace again. 

    The Fan Runs But There’s No Heat 

    While this isn’t an uncommon issue in any sense, it is one that is blissfully easy to troubleshoot. If you’ve worked closely with other models of RV furnaces, you can likely think of a few of these already. 

    Since your Suburban RV furnace is such a complex machine, there could be faults in any of these components. Some of these will overlap with each other, such as the high limit switch and the controller board. 

    The High Limit Switch 

     

    The high limit switch isn’t working correctly. What you’ll want to do is return to your multimeter and check the voltage on the limit switch. If you get a poor reading, that means there’s not enough power reaching the controller circuit. You can test this at both the controller board and the switch. 

    The Controller Board 

    In reference to the controller board, it itself could be experiencing an issue before it even gets to the high limit switch. If the controller board has failed, it will cause the gas valve to not open. When the valve is stuck closed like this, you’ll be able to test it with a multimeter during the turn-on cycle. 

    The Sail Switch 

    The sail switch being unable to close fully is another potential downfall of your Suburban furnace. If this is the case, that means the entire furnace just isn’t getting ample power supplied to it. What causes this is likely the switch getting ‘stuck’ in one position. Another possibility is that the fan isn’t spinning fast enough. The end result of this is nothing but cold air, if any at all. 

    The Gas Valve 

    Another thing that could let the fan run without heat generation is, once again, the fault of the gas valve. It’s possible that it’s not opening, independent of any issues relating to the controller board. If it’s not opening, there’s no gas getting to the combustion chamber. Check the voltage at the gas valve and see if you find a correct reading there. 

    Additionally, the gas valve could be opening, but without any propane flowing through. More than likely, you’ve got something clogging the line. There could also be a lack of pressure present, or a failing regulator. 

    The best way to see if the lack of propane flow is the cause is to test another gas appliance. If it’s not running either, it’s a safe bet that this is the problem. 

    The Igniter 

    A less common culprit, but one worth checking if everything else seems to be working fine. When the igniter doesn’t detect a flame, it will trigger a shutdown in the entire unit. 

    Loose Fittings 

    In any of these parts, one thing that might result in the furnace lighting for only a few second before switching off, is loose fittings. Check the connecting lines to any of these parts on your Suburban furnace and tighten anything that seems too loose. 

    Corrosion could also plague your fittings; be sure to look them over carefully for signs of rust and degradation. While you’re at it, make sure no loose or faulty wiring or pipes are causing the corrosion. It isn’t normal for these parts to wear down easily in a Suburban; there might be bigger issues at hand. 

    The Furnace Turns On And Off 

    You might see that your furnace clicks on fine, but turns off while you’re still left shivering. Just when you think it’s sputtered out for good, it roars back to life. This can be an annoying cycle, one that isn’t at all unheard of. 

     

    There are a few things that you can point to in regards to your Suburban furnace turning on and off. 

    The Thermostat Is Getting An Incorrect Reading 

    Your thermostat tells the furnace when it needs to turn on or off depending on what the ambient temperature of the room is. You usually set this to what degree you’d like to keep your living space at. 

    Depending on where it is situated in your RV, hot air from the duct could be blowing onto the thermostat. This makes it think that the RV is much warmer than it is. 

    Convinced that it has done its job, and with the thermostat in working order, this will turn the unit off. The thermostat cools down, it turns back on, rinse and repeat. Conversely, cold air could be hitting the thermostat instead, making it think the opposite but causing the same problem. 

    If you can redirect your ducts, that will more or less clear this issue up. For the problem of cold air hitting the thermostat, check around the area for any drafts that could be to blame. 

    The Burner Is Going On And Off 

    If your heat exchanger is overheating, the high limit switch will leap into action. This results in a  process called cycling on the limit switch. More often than not, a lack of proper air circulation in the furnace is what is causing it. 

    Usually, that poor circulation is the result of that ever common trouble spot: clogs and dirt. Check any vents or tubes that are exposed for buildups, and clean them out as needed. Sometimes, this bug can be caused by literal bugs; some of the external vents are small enough that one insect can make the entire system go haywire. 

    Speaking of an abundance of dirt, build up of dust will lead to the heat exchanger to make the burner swap between on and off. It’s a common issue, given the direction of air in reference to your furnace. A good dusting with a microfiber cloth will likely clear things up. 

    Finally, the problem with the burner could be traced to the limit switch itself. Check the voltage of the limit switch to see if it’s getting an appropriate supply of power. If you find that the supply is inadequate, you might need to resort to replacing the switch module itself. 

    This might be a tall task to undertake, one that should only be attempted if you’re well versed in how to repair your Suburban model furnace. If need be, reach out to your dealership or a Suburban representative to get their opinion. It might even be less expensive to have someone else replace it, depending on your level of expertise. 

    Furnace Doesn’t Shut Off When The Temperature Is Reached  

    A lot of the issues discussed in this guide have been in reference to the furnace not turning on as it should. You’re left cold, and wondering what the problem is. While there are dozens of things that can go wrong in bringing the heat, that warmth can also become too much. 

    When your Suburban furnace seems to keep running even when your desired temperature is hit, it’s likely that the thermostat is the problem. Check the voltage of your thermostat to the time delay switch. If you detect a voltage, but it is too low, the thermostat might be faulty. 

     

    If you don’t detect any voltage at all, there’s likely a short you should be on the lookout for. The short is probably creating a false voltage, like the one that is coming from the thermostat. 

    Bear in mind, the fan will tend to run for a few minutes even after the temperature is reached. This is completely normal, and there is no action you need to take. 

    The reason for this is that your furnace is protecting itself from cooling off too quickly. If this happens, the contraction of air within the combustion chamber could cause an explosion. 

    You should only try to check this voltage if your thermostat keeps running long after getting your room to the right temperature. If it has been 30 minutes or so, it might be time to take a look. 

    The Furnace Doesn’t Work At Night

    Just like us, the battery supply in your RV can run itself dry and become exhausted. The motor in your furnace needs to heft along a lot of energy to work correctly. If your batteries aren’t strong enough to shoulder that, they could start to drain when they’ve been running through the day. 

    This is especially common if you’re in a colder area and running the furnace frequently. Replacing the batteries could make this less of an issue. Look for ones that are stronger, but still compatible with your RV at large, as well at the converter. 

    Finally, the battery is subject to corrosion. The reactive chemicals inside your battery could hinder the wiring, and cause them to draw power excessively. That will make them run their course far before their time. 

    With a pair of gloves for safety, check over the wires for signs of corrosion. Hints of discoloration, or the feeling that the wire coating has thinned, are indicators that they’re starting to degrade. 

    Soot On The Exhaust Vent

    You might think that a little soot on your exhaust vent is no big deal, and just something to clean up. However, this is actually a signal that a very serious problem is occurring. 

    Finding soot on your exhaust vent is a sign that your Suburban furnace is not combusting cleanly. During improper combustion, carbon monoxide is produced. If you find soot on the external exhaust, DO NOT use your furnace until it has been inspected by a professional. 

    Carbon monoxide is dangerous, even potentially deadly. It is in you and your family’s best interest to not touch your heating system at all until it has been inspected. You might need to replace the entire furnace in this event. 

     

    The Furnace Is Making Noise 

    Suburban furnaces will usually have a distinctive thunk or thump noise when they start up. This is normal, and is usually caused by the gas valve opening. However, if there’s a clicking or grinding noise coming from your Suburban RV furnace, look to the fan. 

    What could be happening is that the fan blades are rubbing or clicking against their housings. That clunk clunk clunk is the repeated sound of those blades whacking into the walls around it. You might need to replace either the fan or the housing. If the problem has been going for a while, you might need to replace both, as the fan is likely damaged by now. 

    If you’re hearing a rattling noise, it could also be a loose bearing somewhere within the fan’s motor. Unless you really know your motors enough to tighten it, it could be easier to just buy a new fan. 

    The Furnace Works On Shore Power, But Not On Batteries

    If you disconnect from city or shore power and hit the road, you’ll of course take all of the comforts of home with you in your RV. You would think that everything ought to work more or less the same as it did when you were safely connected to your campground. 

    However, if you are out on the road and finding that the battery of your RV seems to not be enough to power the furnace, you’re surely looking for answers. If it still works when it is connected to a generator, but not on the battery, you can likely deduce that the battery is the root of your problem. 

    Corrosion might have degraded your battery to the point where it is no longer usable. It could also not be working at full capacity, meaning it isn’t strong enough to get the furnace going. If this is the case, you might notice the occurrence with other appliances too. 

    The best way to remedy this is to just replace the battery. It will likely tidy up some other issues within your RV as well. 

    Tip 

    For a quick guide on troubleshooting your Suburban RV furnace, check out the official troubleshooting flow chart. The charts start on page 30 of this guide book. Be sure to follow the flow chart for the correct type of suburban furnace you have. 

    Conclusion 

    Your Suburban RV furnace is a complex, well designed machine that requires a lot of separate components to work properly. Between the gas valves, the blowers, the motors, and everything else, it take a lot to keep it in fighting shape. 

    These models are durable and dependable. However, when one part of your furnace goes down, the rest will likely follow suit. Make sure you frequently clean and inspect your furnace and all of the vents, tubes, and wires that connect to and from it. This will let you know right away if any issues are starting up. 

    Keeping a vigilant eye on your unit will allow it to warm your RV for many road trips to come, no matter the weather. 

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