Need help with furnace

wa8yxm wrote:

John Wayne wrote:
My guess would be it hasn't been used in awhile and had air in the propane line.

This is another one I hear all the time...

First: The furnace burns gas fast enough that if there were air in the propane line it would be blown out on the 2nd attempt and by the 3rd attempt there would only be propane in the lines.

Second: how did the air get INTO the propane lines? Some folks talk about "Well when you unhook the bottles to change/refill them" true, a teaspoon or two of air can get in then.

But I grew up with propane, 3 different systems on the farm, One for the house, one for the other house one for the milkhouse, and not one of them ever had that problem even when we detached the 100 pound bottles and took them to town (Actually 3 or 4 towns over), not the nearest town) and back to re-fill them and brought them back.

IT all worked fine, Never had so much as a water heater go out due to air in the lines.

One system was a space heater (In fact two were)
One was a water heater and kitchen stove/oven.

Not one of them ever had air-in the line problems.

A lot of these RV systems have very small leaks in them. Not enough to cause a explosion or anything but, enough that if they set around with the valve on the tank closed for a few weeks/months the line can go empty. On my TT in the spring it takes a couple of minutes for gas to reach the stove burners to get them to light. The fridge or furnace will shut down and go into lock out in that amount of time. Once I get the stove to light it only takes 1-2 tries to get the furnace or fridge to light You right though, just changing the tank does not get enough air into the line to make a difference.

John Wayne wrote:
My guess would be it hasn't been used in awhile and had air in the propane line.

This is another one I hear all the time...

First: The furnace burns gas fast enough that if there were air in the propane line it would be blown out on the 2nd attempt and by the 3rd attempt there would only be propane in the lines.

Second: how did the air get INTO the propane lines? Some folks talk about "Well when you unhook the bottles to change/refill them" true, a teaspoon or two of air can get in then.

But I grew up with propane, 3 different systems on the farm, One for the house, one for the other house one for the milkhouse, and not one of them ever had that problem even when we detached the 100 pound bottles and took them to town (Actually 3 or 4 towns over), not the nearest town) and back to re-fill them and brought them back.

IT all worked fine, Never had so much as a water heater go out due to air in the lines.

One system was a space heater (In fact two were)
One was a water heater and kitchen stove/oven.

Not one of them ever had air-in the line problems.

CampingN.C. wrote:

Chris Bryant wrote:
Sounds to me like a pinched copper line, or a bit of debris in the orifice- a restriction to the LP flow.

I think you nailed it. I thought I had it going but it started to act up again. I called the dealer today and before I fully explained the symptoms he said it was debris, which is odd because it's been in a garage all summer, but that's my luck.
Of course it's not covered under the warranty. And of course it cannot be removed from the exterior, lovely !!

I'd suggest to break out the air hose again and this time direct it into the intake port. You could also blow back through the exhaust to make sure any debris is moved out of the ignition area.

CampingN.C. wrote:

Chris Bryant wrote:
Sounds to me like a pinched copper line, or a bit of debris in the orifice- a restriction to the LP flow.

I think you nailed it. I thought I had it going but it started to act up again. I called the dealer today and before I fully explained the symptoms he said it was debris, which is odd because it's been in a garage all summer, but that's my luck.
Of course it's not covered under the warranty. And of course it cannot be removed from the exterior, lovely !!

If it's anything like mine it's easy to remove from the interior though.

Chris Bryant wrote:
Sounds to me like a pinched copper line, or a bit of debris in the orifice- a restriction to the LP flow.

I think you nailed it. I thought I had it going but it started to act up again. I called the dealer today and before I fully explained the symptoms he said it was debris, which is odd because it's been in a garage all summer, but that's my luck.
Of course it's not covered under the warranty. And of course it cannot be removed from the exterior, lovely !!

Sounds to me like a pinched copper line, or a bit of debris in the orifice- a restriction to the LP flow.

John Wayne wrote:
My guess would be it hasn't been used in awhile and had air in the propane line. The heater will try and light 3 times then turnoff and you need to turn off the thermostat and start all over again. When I say tries to light 3 times you will be able to hear the igniter light the flame it will burn for for a few seconds then go out it will do this for 3 times and if the flame doesn't keep going you will have to turn it off and start all over till all the air gets out then it will work with no problems until it has sat for an extended time and air has gotten in the propane line. Been there done that.

That's exactly how it was acting except it wouldn't stop at three. It would just continue trying. No was there's air in the line. The HWH is directly on top of it and was running the entire time on gas. In fact I was running it for that exact reason.
As far as I can tell the compressed air blown up the vent is what got it running. No debris blew out so it's still a mystery to me.

My guess would be it hasn't been used in awhile and had air in the propane line. The heater will try and light 3 times then turnoff and you need to turn off the thermostat and start all over again. When I say tries to light 3 times you will be able to hear the igniter light the flame it will burn for for a few seconds then go out it will do this for 3 times and if the flame doesn't keep going you will have to turn it off and start all over till all the air gets out then it will work with no problems until it has sat for an extended time and air has gotten in the propane line. Been there done that.

sch911 wrote:
Sounds like a bad sail switch.

I love knee jerk reactions.

No, it can not possibly be a bad sail switch else it would not light at all.

Thermocouple yes, Control board, perhaps, Burner adjustment yes, Sail switch no.

The process (Ecerpted)

Stuff happens setting it up to this point.
The sail switch closes (Done)
The control board opens the gas valve, which allows gas to flow and starts generating sparks.

Many Atwood units have a single wire ignition system, In this system the wire carries about 1,000 volts AC to make sparks, and about 1/2 volt ((0.480) DC to sense flame... But we are not yet ready to discuss the problem with that idea.

The flame lights

The flame heats a metal rod, this rod is both the "Spark Plug" and the therocouple. Ideally it starts making .480 volts DC which the control board senses, When the board sees this voltage it says "AH, Working, Let's keep on heating" till it gets a cut off signal (Different cutoffs for different issues but since we are not getting there this is where I will stop)

There is an insect that likes to nest in gas jets, This can block the full flow and cause the unit to not burn hot enough to heat the rod.

The rod can get covered in carbon from a poorly adjusted burner and not heat as fast as it should.

The fuel/air mix (Air damper) may be off causing a cooler than normal flame.

In all 3 of these cases partially obstructing the exhaust may force a higher temp.. But fixing the problem is the better idea.

ALL 3 of the suspects above are cleared by ROUTINE Preventive Maintenance. Nothing more needed.


Finally: it is possible the connection between flame sensor and mother board is not that great leading to a hotter sensor being needed, or that the board is shot or nearly so and not always detecting, but these are low probability issues in this case.

kaz442 wrote:
Pilot light? This is a 2014? Really?

My junk is an 1989 and has electric ignition on heater and hot water.

There are two types of electronic ignition. One type uses a intermittent pilot light. So you can have electronic ignition and a pilot light. Depends on the manufacturer.