Community Forums

Old-Biscuit · 01-03-2023, 05:06 PM

Clarification:

4" should be on sides (rear duct openings)

One 4" on EACH side not same side
Top should not be used except for additional ducts

flbill · 01-03-2023, 05:28 PM

Thanks Old Biscuit!

I will rework the ducts - how would you seal the openings that should not be used? I am thinking electrical plates with aluminum foil tape.

Here is the pic of what Thor says should be...

In my case, there is one 2" on each side, one 4" on each side, and two 4" on the top.

B

Old-Biscuit · 01-03-2023, 06:50 PM

Electric blank plates and foil tape will work

flbill · 01-03-2023, 07:18 PM

Thanks.
I'll get this done in the next few days and report back.
At the least there will be a record for other folks.

B

Old-Biscuit · 01-03-2023, 07:34 PM

Quote:

Originally Posted by flbill

Thanks.
I'll get this done in the next few days and report back.
At the least there will be a record for other folks.

B

Check the temp rating on tape.........Hi Limit Switch is 190*F

flbill · 01-04-2023, 09:19 AM

The latest....

Before re-routing the hoses and taping up holes I figured I should do another couple tests.

- After cooling down overnight, how long does furnace run?
5+/- minutes. Fan comes on, heat comes on, heat goes off, fan goes off.

- After a cool down, remove all hoses. How long does furnace run?
5+/- minutes. Fan comes on, heat comes on, heat goes off, fan goes off.

- Both times, and all other times (it did not "click" before), I knew it was off because I could suddenly smell propane. I could smell it before ignition (but understand this can be normal), but I also smell it after the heat goes off.

- It seems like flame is going out, but propane is not shutting down immediately. (it does after a few seconds it seems).

Questions:
Is the propane smell normal?
Should furnace still shut down with all hoses disconnected? Does it need that pressure to keep running?

Thanks.

flbill · 01-05-2023, 09:42 AM

Today I tried the Old Biscuit suggestion.
- Rerouted all the hoses to match the schematic from Thor and Atwood.
Unfortunately it did not make any difference. Furnace shutdown about 6 minutes in

That said - during the second test (with outside furnace cover removed to make sure of air flow) I was standing there when it shut off - and I heard a very distinct click of a switch.

Thats when I found what I believe is the High Limit Switch.
I remembered an early post stating it could be bypassed (but not for to long) to see if that was the issue.

So I disconnected the two blue wires and jumped them out - and the furnace ran in excess of 9 minutes before I manually shut it off.

In this pic is the view of the switch located directly above the exhaust. You can see it is very corroded which can cause faulty action in any switch.

Is this the high limit? Is it safe for me to simply replace it?

triplewide · 01-05-2023, 12:13 PM

I am not clear on the sequence of events in your field tests. Does the fan run after the flame is out or shut off the same time as flame?

You can replace it with out any problem, costs about $20. This may not be the problem though, still could be low fan speed or return. duct issues.

If it was me? I would throw a $20 part at it and see what happens. (but I am a "part changer") I keep replacing parts until a problem goes away. I would probably change the limit while I'm in there and have it apart just on general principles.

High temp limit on Amazon:

https://www.amazon.com/Switch-Atwood...B68B8SZN&psc=1

flbill · 01-06-2023, 06:27 AM

All systems run normally except for shutting off.

Fan starts first.
Propane ignites - hot air blows.
5-8 minutes in heat goes off.
Fan runs for 30 seconds or so then shuts down.

I will be replacing that switch as soon as it arrives.... hopefully that will be the end of the story.

triplewide · 01-06-2023, 05:12 PM

Good luck, let us know what happens.

Old-Biscuit · 01-07-2023, 08:08 PM

Yes that is the High Temp Limit Switch and those terminals are VERY Corroded which can impede 12VDC

New switch will probably resolve your issue once and for all.

flbill · 01-15-2023, 10:52 AM

OK - following up with this.
I have rerouted the heater hoses according to spec and replaced the high limit switch.
Today - fired everything up and worked fine - shut off just below the temp setting after running for a long time.
- I then turned the thermostat up and the unit came on - blowing air as it should. But propane never lit.

- Turning off the heater (at the tstat) and back on again and everything worked fine...

- repeated this test in various ways a few times... and growing frustrated when I had a thought. I read in a post on heaters that one person found that they had to light the oven burner in addition to a stovetop to make sure all air was out of the lines.

- Wow. I did this and repeated my tests - and it seemed to work like it should.
Now I don't know if it was coincidence, luck or a real.. can anyone shed any light on this?

Should I light the oven and stove before using the furnace?

triplewide · 01-16-2023, 06:58 AM

Quote:

Originally Posted by flbill

OK - following up with this.
I have rerouted the heater hoses according to spec and replaced the high limit switch.
Today - fired everything up and worked fine - shut off just below the temp setting after running for a long time.
- I then turned the thermostat up and the unit came on - blowing air as it should. But propane never lit.

- Turning off the heater (at the tstat) and back on again and everything worked fine...

- repeated this test in various ways a few times... and growing frustrated when I had a thought. I read in a post on heaters that one person found that they had to light the oven burner in addition to a stovetop to make sure all air was out of the lines.

- Wow. I did this and repeated my tests - and it seemed to work like it should.
Now I don't know if it was coincidence, luck or a real.. can anyone shed any light on this?

Should I light the oven and stove before using the furnace?

Probably an Old Biscuit question. I've not had this problem yet. My thoughts are that once the furnace has lit and run up to temperature, you should not have any air in the gas line anymore if you don't have any leaks, gas tank is not low or empty, regulator on tank is working, gas valve on furnace is working. Checking/cleaning wiring connections on the furnace gas valve may be worth doing. When the furnace fails to light, maybe you could check for voltage on the gas valve at the furnace and safely check for gas at the inlet to the gas valve.

Old-Biscuit · 01-18-2023, 02:01 PM

When propane is valved in lighting off the stove top burners helps place the regulator in service to establish flow/pressure in the LP System
*after last appliance is turned off the regulator goes into lockup (14"WC) and using the stove top burners places reg back into control at 11"WC

Smelling of Propane....
Spark electrode should be firing just before propane flows
*Electrode & gas valve get DC at same time....might have SLIGHT smell of propane just prior to ignition
When DC is dropped off gas valve (Flame out and/or thermostat) the gas valve should immediately close and should not have any lingering smell of propane

You stated:
Today - fired everything up and worked fine - shut off just below the temp setting after running for a long time.
- I then turned the thermostat up and the unit came on - blowing air as it should. But propane never lit.
When furnace shut down and you turned thermostat up higher....fan should have come on AND should have reestablished flame

Lighting off stove top burners had no effect as system was already pressurized and regulator was in control....coincidence, luck

Furnace firing up normal, reaching t-stat set point but NOT refiring when t-stat temp setting was raised points to Circuit Board Issue

Bad contacts/connections (DC from Sail Switch/Hi temp Limit to circuit board) of Circuit on the board that sends DC to electrode & gas valve