Furnace troubles

[aartod]

Hello there, my first post... so I have an old 5th wheel trailer I have been fixing up, a '84 alpenlite 28'. So, I tried to get my furnace running, first of all it was missing a ignitor/flame sensor-so I got one an installed it. So when I tried to fire it up it would light for a few seconds then go out. So I figured the flame sensor was not sensing flame. I figured the whole darn thing needed a cleaning and inspection, so I removed it and cleaned up contacts, tested the sail switch & high limit switch, blew out the burner area, cleaned the gas tube & orifice, and tested the soliniod/gas valve. Everything tested good. So next I tested my actual gas pressure and it was low, so I got a new regulator and retested. I now have 11 inches of water ccolumn with other devices running. So I tried to fire up the furnace again and after all the air bled out of the line it fired up and ran fine for a few min then the flame went out. So I turned the thermostat off and on again and it fired up for a few seconds then the flame popped loudly a few times and wouldn't relight. I did this a few different times until it popped really loud and blew a chunk of my flame sensor gasket out. It is a atwood/hydroflame model 82. What could cause this? Flame sensor/ignitor alignment? It is brand new... circuit board issues?(it's the only thing I can't test) Soooo, now I come to the experts for advice!

[aartod]

So, today I blasted all the gas lines out and pulled the burner unit to see how the flame sensor/ignitor was aligned. I adjusted the gaps as specified in the manual, then also tweaked the flame sensor closer to the flame and the ignitor closer. I then retested the gas pressure with my manometer and checked for leaks with the manometer. I turned on the furnace waited for its various start up cycles and it fired up and operated perfectly. I let it run for 15 min and it operated flawlessly. Thanks for all of your comments and suggestions. I imagine the only real problem I had was a ignitor/sensor alinment problem. I am glad that I removed the furnace and preformed the maintenance that I'm sure the unit needed anyways...

[Harvard]

aartod wrote:
The one thing I have not tested is the actual Gas pressure at the furnace. I tested the gas pressure at the stovery due to the ease of hooking a manometer to it. I need to purchase a fitting to test it at the furnace. Unfortunately, the nearest store is quite a drive.

Apply soapy water as you start to disconnect the connection at the furnace WHEN the furnace is not working might tell you something..

[aartod]

The one thing I have not tested is the actual Gas pressure at the furnace. I tested the gas pressure at the stovery due to the ease of hooking a manometer to it. I need to purchase a fitting to test it at the furnace. Unfortunately, the nearest store is quite a drive.

[aartod]

I did, and read thru it. I am just seeking and advice I can from people who have been there done that. I will adjust the flame sensor/ignitor assembly as shown in the manual and make sure the flame sensor is completely engulfed in flame. I know all the wiring is good and all contacts have been cleaned and tested for continuity.

[Old-Biscuit]

Download the manual in link and read it/follow it......it even has pictures

[aartod]

So, from my reading and forum suggestions, I will blow out my propane lines/plumbing and adjust the ignitor/flame sensor today. Maybe I ought to tweak the ignitor and flame sensor close to the burner as well. What I have learned is that these explosions can be caused by excess propane build up or a lean gas mixture (clog in line, low pressure). Also I have read that a dirty burner can cause this, but I have already cleaned it out and when it did light the entire burner was lit evenly. If anyone else has any knowledge of furnaces please let me know other potential areas to investigate.

[aartod]

Thanks, oldbuiscuit, I will check on those dimensions tomorrow.

[Old-Biscuit]

Loud popping is from an accumulation of unburnt gas

Ignitor Gap needs to be 1/8" and centered over burner slots
Flame sensing rod gap is 3/8" and needs to be engulfed in main flame when it lights off

1980s Hydro Flame manual
Pg 34

[Lwiddis]

“is that the approved method?”

Who knows on a 35 year old RV furnace? Go to a pro.

[aartod]

No, I did not. I am extremely new to the rv/trailer world, so I did not even know of such things. Can I remove the regulator and blow out the gas line (also disconnect the furnace), is that the approved method?

[Lwiddis]

Might be time to throw in the towel and take it to a pro who is willing to let you watch the repair and explain.

[Harvard]

Did you verify that there are no oil filled p traps in the gas line to the furnace?