Furnace Problem Observation

**sourdough** · 01-21-2020, 03:58 PM

It is wintertime and from time to time there are different posts about various problems with furnaces. Sometimes they are pretty clear cut; I've replaced fans, control boards etc. But something a little sneaky happened to me last night that might be valuable to tuck away if one isn't aware.

A year or so ago I put the little mesh "bug screens" over my hot water heater and the exhaust on the furnace. Never had a bug get in either but thought I would be proactive. Last winter the furnace sort of acted weird but continued to heat and function. Last night got pretty cold for here (about 31) and the furnace was running quite a bit, until I woke up about 3am freezing. Wondering what was going on I listened for the furnace; the fan was running but the burner would only kick on for a few seconds then go back off. The air would not get warm. It did not cycle off, just kept firing up, burner run for a few seconds then stop. Turned off the thermostat thinking that would be the issue (replaced 4 times at the moment) but didn't fix it. Turned on the fireplace and a little heater and went to sleep figuring I would look at it today.

This morning turned on the thermostat and it fired up, kept blowing, got hot and heated the room. On the 2nd attempt to fire up and run it did the same thing it did during the night. Fan comes on, burner kicks in full blast, runs a few seconds and shuts down. Thinking through it I figured it was the limiting switch so opened up everything dreading tearing that thing apart...and then, a thought (somewhat rare these days)!! Limit switch faulty? Limit switch "activated"? It wants input, output and through put. Now you know where I'm going.

Out of curiosity I went outside and removed the mesh screen from the heater exhaust cover. A fairly fine mesh thinking it might be causing the heat to back up running as much as it was. Ran all day today and all evening without a hiccup so figure that was it. I'll know 100% in the morning but as consistently as it was failing I'm 99% sure. Just wanted to throw that out in case someone might fall into a similar predicament. Looks like it saved me tearing that furnace apart and I'm all about that.

CedarCreekWoody · 01-22-2020, 04:31 AM

Was the screen visibly obstructed? Those are not typically a fine mesh.

**sourdough** · 01-22-2020, 06:45 AM

No obstruction whatever. Looked brand new except for the discoloration from the heat in the center. Ran just like it was supposed to last night so took care of the problem. I figure it provided just enough blockage to the exhaust that it caused the furnace to get too hot and the limit switch to shut it down. It's a 35k unit and it puts out a lot of exhaust. Below is a link to the screen I have. It's not as fine as a door screen but I suppose a lot more restrictive than the exhaust being wide open.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

CedarCreekWoody · 01-22-2020, 06:57 AM

That is what I run too. Not encouraging.

**sourdough** · 01-22-2020, 07:35 AM

Easy enough fix; it took only about 5 minutes to pull the cover and remove the screen. It's not a big deal for us because the unit is either in use or stored in a "bug free" storage facility. It might be an issue if the trailer is left outside unattended in bug country.

**chuckster57** · 01-22-2020, 07:41 AM

We use this style. Never had a comeback yet.

https://www.amazon.com/TOODOO-Flying...18895821&psc=1

spade117 · 01-22-2020, 08:20 AM

Quote:

Originally Posted by chuckster57

We use this style. Never had a comeback yet.

https://www.amazon.com/TOODOO-Flying...18895821&psc=1

Same here.

CedarCreekWoody · 01-22-2020, 08:20 AM

Quote:

Originally Posted by chuckster57

We use this style. Never had a comeback yet.

https://www.amazon.com/TOODOO-Flying...18895821&psc=1

That is actually what I have. Maybe I misunderstood what Sourdough was using as mine is not a fine mesh.

**sourdough** · 01-22-2020, 10:15 AM

Mine is an Atwood furnace. The little mesh ball is about 2 1/4" or less so the one in the attached link would be too large to fit. It also indicated it was for a Suburban. The additional mesh on the sides are to cover the other grill vents that would be left open.

**chuckster57** · 01-22-2020, 10:55 AM

There are different screens held on by the enclosed spring. One will fit your furnace so there isn’t any “taking apart” of anything.

**sourdough** · 01-22-2020, 12:04 PM

Yep, got one on my hwh. Those little spring doo bobbers are heck on my Atwood (hwh) to put on and take off with that little tool. I may try to find one just to try it. I've never had an insect get into anything on the RV but there's always a first time....and I would like to never have that happen.

**JRTJH** · 01-22-2020, 12:28 PM

Danny,

The Suburban furnace installation manual has a warning about NOT using any screen over the exhaust/intake vents on the trailer sidewall. It seems to me that same warning was in the Atwood/HydroFlame manual "years ago". The last Atwood furnace I had was in a 93 Holiday Rambler, so I'm sure things have changed since then.

Anyway, that warning is still in the Suburban furnace guide. For that reason and, like you, I've never had a problem with insects getting in the furnace "combustion vents" I just use aluminum foil "ducting tape" and cover them during storage. It's a simple matter to pull the tape off in the spring and slap another 6" strip on the vent in the fall.

Now, if I had a "persistent problem with insects" I might rethink my plans, but since I don't have that problem and do have a Suburban furnace, I try to follow the warnings in the manual.

With the Atwood, the install guide I've got doesn't address the vent screens, I'm going to check for an operator's guide to see what that has in it, but I don't have one handy, got to go "web searching".... More to come.

B4Keystone · 01-22-2020, 12:52 PM

Does it not take more time and worry to try and prevent the problem than actually deal with it when/if it ever happens?
Just saying.
Lol

**chuckster57** · 01-22-2020, 01:02 PM

Quote:

Originally Posted by B4Keystone

Does it not take more time and worry to try and prevent the problem than actually deal with it when/if it ever happens?
Just saying.
Lol

If it does happen, mud dawbers will make a nice mud nest right on the burner. It won’t light and you have to dis assemble the entire furnace to get rid of the nest. I’ll let you decide which is better, we get about 3 Hrs labor.

**flybouy** · 01-22-2020, 01:07 PM

I've never had an issue with mud daubers. Their favorite food supply are spiders so I do my best to keep any spider webs off the camper by using the flea collar from the dog (the old when after replacing it) in the bottom of the outside fridge compartment and hot water heater compartment. This seems to work well and any other spider webs get dispatched with a broom.

**sourdough** · 01-22-2020, 01:09 PM

Quote:

Originally Posted by B4Keystone

Does it not take more time and worry to try and prevent the problem than actually deal with it when/if it ever happens?
Just saying.
Lol

No, prevention is the answer. I've not torn this furnace apart, but I've had to tear one apart and don't want to if I can prevent it. The screen is a really simple thing but I can see now how just that small amount of restriction puts the furnace into a tizzy. If I need to I'll use something like John suggested. When unused I keep it in a sealed, insulated storage facility that doesn't have flying critters so not sure it's even warranted.

**chuckster57** · 01-22-2020, 01:13 PM

Wish I had taken and kept pictures of some of the furnaces I’ve taken apart.

**JRTJH** · 01-22-2020, 01:17 PM

Here's the warning as it's printed in the Operator's Manual for the Atwood/Hydro Flame furnace:

POSSIBLE INJURY OR DEATH
Do not install screens over the intake air or exhaust vents for any
reason. Screens will become restricted and cause unsafe furnace
operation. Accessories are being marketed for RV products which we
do not recommend. For your safety, only factory authorized parts are to
be used on your furnace.

It's located on Page 2 of the manual: https://www.manualslib.com/manual/12...?page=2#manual

It's stated this way in the Suburban manual:

WARNING! Do not install screens over the vent for any reason. Screens will become restricted and cause unsafe furnace operation. Accessories are being marketed for RV products which we do not recommend. For your safety, only factory authorized parts are to be used on your furnace.

In the Suburban manual, it's located on Page 7, near the top.
http://bryantrv.com/docs2/docs/SFseriesservice.pdf

I'm not suggesting that anyone should "run outside and rip their screens off the furnace vent or they might die.... I'm just stating what the manuals for Atwood and Suburban furnaces provide in a warning in the operator's manual.

**sourdough** · 01-22-2020, 03:26 PM

Thanks John. I had read that but to me it said the screen "will" become restricted to me indicating they thought that something would clog it up, which I was prepared to fix....but this one is/looks new. The takeaway to me is that it really means don't put ANYTHING over that exhaust....and I'm a believer now. It may not be the same with a 30k unit, I don't know but it sure put a damper on this one.

CedarCreekWoody · 01-23-2020, 04:49 AM

I've had dirt daubers block the burner tube on my hot water heater. It still worked but put black soot up the side of the camper. I had to disassemble it to clear them out. I now use the coarse mesh screen on the HWH, the furnace, and the fridge. I've never seen the screen build up any type of obstruction. That is why I found Sourdoughs experience interesting when he apparently encountered issues with no visible screen obstruction.

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