How to service a furnace?

[bogen2]

I have a good idea on how to service most of the components of my rig, but as I was getting it ready for our winter travels I realized I had never looked at the furnace. So I pulled the cover off the outside to look at how I might service the more common problems noted in other threads, like the sail switch, flame sensor and control board. After looking at it I don't have an idea how to do any of them. I assume that the sail switch is the connection at the front but I don't see how it would be removed. I don't see access for the flame sensor at all and the control board is at the top and looks inaccessible from the outside.


So I would appreciate any insights into doing troubleshooting and repairs on this unit. I googled for a service manual but only found installation instructions.

Bob

[howson]

bogen2

I haven't pulled the furnace out of my 315RLTS, either. The only "service" I do on a regular basis is ensure the intake and exhaust tubes are clear of debris. I also perform a "test fire" to ensure there's no issues before a trip where I suspect the furnace will be needed.

If servicing of the furnace is required, what I learned at the RV technical school is that removal of the unit is the norm. I'm leaving that task until the day comes when I have to do it.

For more on the sail switch, see https://gdrvowners.com/forum/operati...on-the-furnace

To get manuals, check the RV Works website. He's done a great job organizing manuals: https://myrvworks.com/manuals/

Howard

[Country Campers]

In order to service you would need to remove the whole furnace. Unhook the duct work on the back, the propane line making sure that the propane is off, and also the 12 v dc power connection, making sure all power is removed before. Then there should be a couple screws on the top and bottom, maybe, that hold the unit in, remove those and out she slides. You may not have to remove the duct work as there is an outer shell that the furnace unit slides into and if that shell can remain then the duct work can stay attached.

Brian

[colan]

Removing a newer vertically mounted Suburban furnace is a pain.

The horizontally mounted units have a a screw at the back accessible after removing the plate holding the rear vent hoses. The vertical mounted unit have the same screw.

At the front after removing the outer cover is another screw on both the vertical and horizontal units.

NOW THE HARD PART - a vertical mounted unit is a slightly different model with more screws in the furnace from the outer case to the inner. Oftentimes these screws are located where it is impossible to access the screws. Ok, so remove the entire furnace, case and all after disconnecting all of the hoses- if it were only that easy. Furnace is held in place with a couple of 90 degree L brackets. If you can remove the L brackets from the furnace. Sometimes it is really difficult to get at the screws on the L bracket into the furnace. Okay, (there is a catch) so just remove the other screws in the bracket leaving the brackets attached to the furnace. Next problem, trying to slide the unit out the hole with the L brackets still attached is difficult at best. Opening is too small!!!

All of that said, pull the outside cover, do some light cleaning, inspect the intake and exhaust with a flashlight and call it good.

[Guest]

I have a good idea on how to service most of the components of my rig, but as I was getting it ready for our winter travels I realized I had never looked at the furnace. So I pulled the cover off the outside to look at how I might service the more common problems noted in other threads, like the sail switch, flame sensor and control board. After looking at it I don't have an idea how to do any of them. I assume that the sail switch is the connection at the front but I don't see how it would be removed. I don't see access for the flame sensor at all and the control board is at the top and looks inaccessible from the outside.


So I would appreciate any insights into doing troubleshooting and repairs on this unit. I googled for a service manual but only found installation instructions.

Bob

Bob,

This is very interesting where I would like to see how you go about doing this. The seasonal check on a home furnace would be to check the cleanliness of the squirrel cage blower, sail switch on our application, burner (s) and a combustion check. The combustion check would be over the top and requires an expensive meter as in the example below. Flame sensors can be cleaned with some emery cloth an nothing more. I purchased a Fieldpiece manometer to avoid being scammed by some HVAC folks if there is a simple issue such as a pressure switch or induction blower. Seems the go to phrase from some unscrupulous techs to sell a new unit is that the heat exchanger is cracked when it is not. Disgusting.

https://www.amazon.com/Testo-0563-31...13274178&psc=1

Jim

[Scott'n'Wendy]

Removing a newer vertically mounted Suburban furnace is a pain.

The horizontally mounted units have a a screw at the back accessible after removing the plate holding the rear vent hoses. The vertical mounted unit have the same screw.

At the front after removing the outer cover is another screw on both the vertical and horizontal units.

NOW THE HARD PART - a vertical mounted unit is a slightly different model with more screws in the furnace from the outer case to the inner. Oftentimes these screws are located where it is impossible to access the screws. Ok, so remove the entire furnace, case and all after disconnecting all of the hoses- if it were only that easy. Furnace is held in place with a couple of 90 degree L brackets. If you can remove the L brackets from the furnace. Sometimes it is really difficult to get at the screws on the L bracket into the furnace. Okay, (there is a catch) so just remove the other screws in the bracket leaving the brackets attached to the furnace. Next problem, trying to slide the unit out the hole with the L brackets still attached is difficult at best. Opening is too small!!!

I've never had the need to remove any furnace from my RV's...it's really that much of a PITA? The fridge is easier..lol
Really, I expected there to be like maybe two screws holding it in.

[Cate&Rob]

You guys have furnace service really easy . . . compared to the early build Reflections and Solitudes. On my Reflection, there is no external furnace access panel . Only the exhaust port. The furnace has to be removed from the inside. If you have ever looked behind your furnace, you will realize all the other stuff that has to be removed first.

A large part of my complete plumbing system rebuild several years ago, was getting everything out of the way or removable in the exit path for the furnace. This included relocating the gate valve pull cables to below the floor, routing water lines and wiring up and over the furnace and putting rubber sleeve disconnects in parts of the drain plumbing. The water pump, accumulator tank, TV coax, furnace ductwork and propane lines will still have to be removed to get to the furnace.

I do recall stories of dealers tearing apart interior cabinetry to get to the furnace. Not Grand Design’s best design choice.

Rob

[colan]

“flame sensors can be cleaned”

There is no need to clean the flame sensor as the end gets hot enough to glow red, it is self cleaning. And unlike a photo electric sensor the igniter/flame sensor doesn’t actually “see” the flame.

The rod type flame sensors/igniters work through a process called flame rectification, the flame induces a small current detected by the control board.

Another reason not to clean the flame sensor on some furnaces (Suburban) accessing the flame sensor usually requires opening one or more gas couplings and replacing a fiberglass gasket.

Bob,

This is very interesting where I would like to see how you go about doing this. The seasonal check on a home furnace would be to check the cleanliness of the squirrel cage blower, sail switch on our application, burner (s) and a combustion check. The combustion check would be over the top and requires an expensive meter as in the example below. Flame sensors can be cleaned with some emery cloth an nothing more. I purchased a Fieldpiece manometer to avoid being scammed by some HVAC folks if there is a simple issue such as a pressure switch or induction blower. Seems the go to phrase from some unscrupulous techs to sell a new unit is that the heat exchanger is cracked when it is not. Disgusting.

Ty https://www.amazon.com/Testo-0563-31...13274178&psc=1

Jim

[bogen2]

Well I guess given how difficult it is to service these furnaces, I’ll just hope for the best. I feel like I can DIY pretty much any other system, even while on the road, but the furnace seems like it might be too much to handle, at least for me.

Bob

[Jlawles2]

Actually if the flame sensor can get dirty and not self clean. Found this out on the home on demand HWH. The procedure for cleaning is not to use any type of san paper, but simply use steel wool. Less likely to leave behind the abrasive that can cause issues with the sensor.

[Guest]

“flame sensors can be cleaned”

There is no need to clean the flame sensor as the end gets hot enough to glow red, it is self cleaning. And unlike a photo electric sensor the igniter/flame sensor doesn’t actually “see” the flame.

The rod type flame sensors/igniters work through a process called flame rectification, the flame induces a small current detected by the control board.

Another reason not to clean the flame sensor on some furnaces (Suburban) accessing the flame sensor usually requires opening one or more gas couplings and replacing a fiberglass gasket.

Colan,

They can be cleaned where I would only do so if I was in there. Or replace it. The flame sensor will built up a coating from combustion which could skew its operation. I've seen this on my propane home furnace in my last residence and before replacing the entire system when natural gas came through.

Jim

[Scott'n'Wendy]

Actually if the flame sensor can get dirty and not self clean. Found this out on the home on demand HWH. The procedure for cleaning is not to use any type of san paper, but simply use steel wool. Less likely to leave behind the abrasive that can cause issues with the sensor.

No, ..... The flame 'sensor' is actually a flame rod that doesn't 'see' flame. the soot you may be wiping away will not make a difference.

Flame rods are actually pretty cool.
The ignitor and the flame rod are actually the same part...at least they are in my furnace

[howson]

I'm not familiar with any other furnace flame sensing device or how they may work so what others have said here could absolutely be true for other appliances, but I can echo colan 's comments in his post above that the flame sensor in an RV furnace conducts an electrical current through the flame. Never once in school did we discuss cleaning of the device. I honestly can't remember one post about a failed or dirty RV furnace flame sensor...though that's just anecdotal and I get that.

[Guest]

Howard,

They get cleaned in the home furnace business all the time. Maybe it does not apply to RV furnaces. But then again seasonal maintenance does not as well as in a home furnace. The one time I had to do this (I've seen many) I used a very fine Emory (ultrafine) cloth but as Joseph has stated, a fine steel wool would be preferred. Its not really carbon black that builds up on the sensor but other chemicals from combustion which is white in color. The flame sensor is basically a thermocouple.

https://www.wikihow.com/Clean-Furnace-Flame-Rod-Sensors

https://prohvacinfo.com/furnace/how-...-5-step-guide/

Jim

[Scott'n'Wendy]

Howard,

They get cleaned in the home furnace business all the time.

That would depend on the furnace. Probably most out there don't have flame rods. And the ones that do, and need to be cleaned? Have a combustion or location problem.
I clean the CAD cell flame sensor in my furnace annually.


I'm thinking we have taken this discussion WAY past what the OP was asking...lol