Furnace runs erratically - Help

[escape artist]

Hi: ChuckBC... I don't have to leave home to get "Heat". Alf
escape artist N.S. of Lake Erie

[Big Sky Camper]

Thanks everyone for your help. I’m buying a simple thermostat today. I tried 3 different sail switches. All behave differently. One runs erratically as previously mentioned with clicking from the sail switch. The second lets the fan run for 30 seconds and shuts off when burner does not fire. The third has the fan run continuously without the burner firing. All three have the red light on the circuit board blink once every 10 seconds or so. Any more ideas with this info. Thanks In advance.

[Vermilye]

While I don't suspect this is your problem, I had the same symptoms with the furnace in my 2017 21. Unfortunately, old enough that you needed to pull the furnace to get to the sail switch (which was the suspect).

With the furnace in the shop, running it determined that it was not the sail switch, but most likely the board. When they pulled the board they found a 1 1/4" flat head screw under the board (the same screw used to hold the wooden surround behind the furnace grill).

Somehow it didn't destroy the board, and after removal & reassembly, the furnace worked great for the rest of the winter.

[Big Sky Camper]

Thanks. I will remove the board and see if any screws are floating around. The noise is a clicking sound from sail switch but there is also a rattle and an occasional clank. I may call dometic tomorrow and see what they say. I hope it stays above 40 tonight. Thanks

[ChuckBC]

Originally Posted by Big Sky Camper

Thanks. I will remove the board and see if any screws are floating around. The noise is a clicking sound from sail switch but there is also a rattle and an occasional clank. I may call dometic tomorrow and see what they say. I hope it stays above 40 tonight. Thanks

Wondering if you tried removing thermostat from equation by doing what Ron said to take 2 wires and jump ignition sequence?

[rubicon327]

Originally Posted by ChuckBC

Frustration is that I had similar problem with a boat with a hydronic heater, a motorhome and now the trailer. My wife wants heat with no problems so this is now priority #1 for happy life.

Rip out the Dometic and go with a Propex or other?

[Big Sky Camper]

If I remove the thermostat are there only two wires to cross? Are there more than two wires there. I want to make sure what I am doing. I will give it a shot when I get back to camp tonight. Actually I will try it in the am.

[rubicon327]

Originally Posted by Big Sky Camper

If I remove the thermostat are there only two wires to cross? Are there more than two wires there. I want to make sure what I am doing. I will give it a shot when I get back to camp tonight. Actually I will try it in the am.

Two wires only. The thermostat is really just a switch that makes and breaks a circuit.

[John in Santa Cruz]

I just read up on that 'anticipator' adjustment (I think clled it hysterisis). Atwood says it shoudl be above 0.48 and even as high a 1.0, this will leave the heater on longer on each cycle, and teh cyles will be fewer and farther in between. Apparently below about 0.4 can cause the thermostats nichrome resistance wire to burn out?? weird, mine has been around 0.15 or 0.2 for a long time.

that digital thermostat mentioned above is starting to look more attractive. I hate the boinging click sounds this one makes. Apparently digital thermostats dont need an anticipator, they just work.

[alanmalk]

...
Apparently digital thermostats dont need an anticipator, they just work.

They have the "digital equivalent". The unit mentioned earlier in the thread does this by ensuring a minimum of 5 minutes in each cycle. So if the furnace is off, it will stay off for a minimum of 5 minutes, and when on, will stay on for 5. My guess - this is designed to protect the furnace, not the thermostat. Perhaps someone can verify that?
--
Alan

[steve dunham]

In a conventional furnace using a standard analog thermostat the anticipator is normally set at .4 to .6 amps which corresponds to the current draw shown on the gas valve
With a digital thermostat and a furnace with an electronic control board there is no reason to have an anticipator setting because the current flow through the thermostat is very small
My furnace had similar issues and the I traced the problem to a defective circuit board
They now have an updated circuit board as a replacement which makes me believe that Dometic had issues with the original board design

[rubicon327]

Originally Posted by alanmalk

They have the "digital equivalent". The unit mentioned earlier in the thread does this by ensuring a minimum of 5 minutes in each cycle. So if the furnace is off, it will stay off for a minimum of 5 minutes, and when on, will stay on for 5. My guess - this is designed to protect the furnace, not the thermostat. Perhaps someone can verify that?

On Lux digital thermostats that I have used you can set what is called the swing which is how tightly it will control to your set point. There needs to be a small temperature range that brings the furnace on and off. Same as cut-in and cut-out pressures with an air compressor. The minimum run times I believe are usually for cooling only to protect compressors.

[steve dunham]

Back in the days before digital thermostats, I installed thousands of Honeywell T87 thermostats , which at the time were the industry standard
They were mechanical , accurate to + - 1 1/2 degrees and were almost bullet proof
The idea that all mechanical thermostats are junk and that all digital thermostats are far superior is BS IMHO
The mechanical thermostat that Escape installs is nowhere near the quality of many mechanical thermostats currently in the market
The reason they are installed is because they are CHEAP

[John in Santa Cruz]

Originally Posted by gbaglo

I installed this one.
No loud click before it sends signal to the furnace to start or shut down. Lighted display.
I'm a happy camper.

I just received that RTH5100B ... its got 6 screws and talks about 4-5 wires, but nowhere in the instructions does it show a 2-wire heat only configuration like ours ? I see there's a mode setting for heat-only, thats fine, but the wiring instructions don't explain what the wires are for....

OK, never mind, I googled thermostat wiring, and R (green) is 'power', while W (white) is heat, so that is all that is connected here, which is what I can see from your picture, doy!

Settings on this thermostat for our configuration: 1(mode) = 2 (heating only); 5(heating system type) = 9 (electric furnace); 14(F vs C) 0 (F); 27 (max heat) = 77 (whatever you want, I don't ever want the heater running much above 72 or 73).

huh, honeywell says the RTH5100B is discontinued, replaced with the RTH5160D1003

[John in Santa Cruz]

Originally Posted by steve dunham

The mechanical thermostat that Escape installs is nowhere near the quality of many mechanical thermostats currently in the market
The reason they are installed is because they are CHEAP

I suspect the reason Escape installs an ATWOOD thermostat with an ATWOOD heater, is thats what it comes with. My biggest complaints about this ATWOOD are A) its nearly impossible to see the thermometer, and the temp adjustment scale has no calibrations (I put 3 tiny strips of black tape on mine for 'low' 'med' and 'high' where high was about 72, and low was about 63 where I like to sleep. My other minor complaint was the distinct TINGGG sound it makes when it switches on.

[rubicon327]

Originally Posted by John in Santa Cruz

Settings on this thermostat for our configuration: 1(mode) = 2 (heating only); 5(heating system type) = 9 (electric furnace)

John: For Installer Setup #5 (Heating Cycle Rate) why not setting 5 which is "gas or oil furnace - (less than 90% efficient)"?

[John in Santa Cruz]

Originally Posted by rubicon327

John: For Installer Setup #5 (Heating Cycle Rate) why not setting 5 which is "gas or oil furnace - (less than 90% efficient)"?

gads, yer right, I have to go check what I set, hah hah. we're in a heat wave, and my brain shuts down when its over 90F and muggy out :-/

[John in Santa Cruz]

anyways, i've tested this honeywell digital thermostat and it works great.

yeah duh, i must have been braindead when I selected 'electric' (I was thinking of the fan). reset it for gas/oil, and have tested it this evening, set it for 69F (its about 60F outside), and its holding the temp quite nicely, I just ticked it up to 70F, and a few seconds later, i heard a faint click, and the furnace came on.

[cpaharley2008]

Frustration is that I had similar problem with a boat with a hydronic heater, a motorhome and now the trailer. My wife wants heat with no problems so this is now priority #1 for happy life.
I see an electric blanket in your future.........

[alanmalk]

Originally Posted by cpaharley2008

Frustration is that I had similar problem with a boat with a hydronic heater, a motorhome and now the trailer. My wife wants heat with no problems so this is now priority #1 for happy life.
I see an electric blanket in your future.........

I love our electric blankey.

For 110 VAC power when boondocking I use a small handheld inverter (also charges various gadgets). The blanket says it needs 120 watts per controller. Wife sets her side independently of mine. With two somewhat warm bodies and a down comforter the unit probably runs at a 25% duty cycle. A few hours of solar is all it takes to replace what was used. No furnace noise! What's not to like?
--
Alan