Furnace Question

[COYota]

Hi All,

The forced air gas furnace in my '84 Sunrader has been making a noise lately that has me a little concerned. When it starts up, first the fan runs for a little while, then there's a muffled "whoomp" sound when the gas ignites, then sometimes there's a metallic bang. Sounds like it could be loose sheet metal hitting something. I've been avoiding using the furnace 'til I get that figured out. Could it be taking too long to ignite, causing a small explosion as it lights, or is there just something loose? Is it dangerous? Any recommendations? I'd rather avoid paying the RV place to diagnose it if its something simple.

-Brad

[Tundrawolf]

Hi All,

The forced air gas furnace in my '84 Sunrader has been making a noise lately that has me a little concerned. When it starts up, first the fan runs for a little while, then there's a muffled "whoomp" sound when the gas ignites, then sometimes there's a metallic bang. Sounds like it could be loose sheet metal hitting something. I've been avoiding using the furnace 'til I get that figured out. Could it be taking too long to ignite, causing a small explosion as it lights, or is there just something loose? Is it dangerous? Any recommendations? I'd rather avoid paying the RV place to diagnose it if its something simple.

-Brad

I have a few questions for you.

1. Is it a pilot lighted furnace? Or, is it electronic ignition?

2. Are you able to observe the ignition process from a safe distance?

I ask these because I had some trouble with my on demand water heater. It is electronic ignition. The ignitor developed a high voltage leak and didn't jump spark until gas had actually leaked quite a distance away from the heater. I was brushing my teeth when I heard an explosion, like a bomb going off, and saw the wall bubble out like someone kicked it.

Now, if you are having this trouble you really need to stop using the furance right away. Has the muffled whump sound always been there? If you are not sure, stop using it! If it has a pilot light, if the orifice has become enlarged, then it could be letting more gas in that it should, and when it finally ignites, it gives a whump sound. The fix could be very simple and cheap (Replacing the orifice). As far as the tin sound goes, take a look inside the heater and grasp sheet metal and see if anything is loose.

[COYota]

I have a few questions for you.

1. Is it a pilot lighted furnace? Or, is it electronic ignition?

2. Are you able to observe the ignition process from a safe distance?

I ask these because I had some trouble with my on demand water heater. It is electronic ignition. The ignitor developed a high voltage leak and didn't jump spark until gas had actually leaked quite a distance away from the heater. I was brushing my teeth when I heard an explosion, like a bomb going off, and saw the wall bubble out like someone kicked it.

Now, if you are having this trouble you really need to stop using the furance right away. Has the muffled whump sound always been there? If you are not sure, stop using it! If it has a pilot light, if the orifice has become enlarged, then it could be letting more gas in that it should, and when it finally ignites, it gives a whump sound. The fix could be very simple and cheap (Replacing the orifice). As far as the tin sound goes, take a look inside the heater and grasp sheet metal and see if anything is loose.

Hi T-Wolf,

Thanks for the reply. It has electronic ignition, no pilot. I don't see a brand on it, but the exterior vent cover says Suburban, so I suspect that its a Suburban furnace. As far as I know, the muffled whump is the normal sound of the gas igniting. The bang is nothing like a bomb going off, just want to make sure that its not heading in that direction. I am not using the furnace until this is figured out. I have observed the ignition process, but I'm not sure what distance is safe at this point.

-Brad

[Maineah]

They all make a little sound when they light no pop or bang. Kind of like the sound of a gas home water heater. If you have any fear of some thing going wrong then you need to have some one check it out for you an RV place maybe kind enough to have a listen to see what they think. I slept in a friends 5th wheel last winter and his heater first sounded like a jet taking off then some thing like a Besamer converter when it lit but it heated the camper just fine, tough to sleep through but warm.

[ranger]

Hi T-Wolf,

Thanks for the reply. It has electronic ignition, no pilot. I don't see a brand on it, but the exterior vent cover says Suburban, so I suspect that its a Suburban furnace. As far as I know, the muffled whump is the normal sound of the gas igniting. The bang is nothing like a bomb going off, just want to make sure that its not heading in that direction. I am not using the furnace until this is figured out. I have observed the ignition process, but I'm not sure what distance is safe at this point.

-Brad

Had a very similiar problem with a furnace in a travel trailer I had. It appears that condensation had created rust in the slots/holes on the burner directly below the igniter. Therefore, gas would not be directly below the igntion area and had to build up from the other slots in the burner and then igntion would happen with a BOOM.

I had to remove the burner and clean with a wire brush and re-intstall. Worked great after that. Hope this helps.

Ranger

[Tundrawolf]

I'd say a safe distance, if it is igniting normally, is maybe 2' away, but I am not an expert. You want to look for flames temporarily licking where they shouldn't when it first ignites. If it ignites normally you may not have a problem. I know a lot of furnaces will click and tink a lot while turning on/off.

[desertrat]

I agree with Ranger. My 1988 suburban heater made all sorts of weird noises. Actually, it wouldn't light at all. I decided it had to be replaced, yanked it out, threw it (gently) on the concrete, and roughed it up. I scrubbed the burner vents, removed the wasp nest, blew it out with compressed air, vaccumed it, threw it together and installed it with no hope of it working again. Guess what? It worked like brand new. Be detatched, yank it out, throw it on the concrete and start cleaning. Scrub the burner vents, vaccum out the dirt, beg it and plead with it that this abuse will stop if it will only work and keep you warm.

Good Luck and let us know

[COYota]

Hi all,

Thought I'd follow up on my furnace issue. Looks like DesertRat had it about right.

I decided to pull the furnace out to give it a look. Found that it wasn't fastened down at all and that the support under it had come un-stapled from the outside wall and collapsed.

I rebuilt the support shelf and blew a ton of dust out of the furnace. I also replaced the old brittle wires between the thermostat and the furnace with a chunk of lamp cord.

After putting it all back together, everything works fine. No banging or other suspicious noises.

Thanks to all for your suggestions.

Brad

'84 Sunrader 180D

FtC CO

I agree with Ranger. My 1988 suburban heater made all sorts of weird noises. Actually, it wouldn't light at all. I decided it had to be replaced, yanked it out, threw it (gently) on the concrete, and roughed it up. I scrubbed the burner vents, removed the wasp nest, blew it out with compressed air, vaccumed it, threw it together and installed it with no hope of it working again. Guess what? It worked like brand new. Be detatched, yank it out, throw it on the concrete and start cleaning. Scrub the burner vents, vaccum out the dirt, beg it and plead with it that this abuse will stop if it will only work and keep you warm.

Good Luck and let us know