Regulator or the gas vlave, Or something else?!

Hi There:
I have this issue with our furnace for the past year that it doesn't come on all the time. The problem seems to be temperature related. In colder weather the heat doesn't come on despite the blower/fan keeps going. There is a chance that I might have two issues which I explain below. First thing to know if that  have replaced the sail switch, fail/safety switch twice with no change. I have also upgraded the circuit boar with Dinosaur brand last year. The problem has been that the fan keeps going, heat/furnace tries to kick in but most of the time it won't stay on despite the fan continues to operate. As I mentioned above, when the weather is warmer, 60-70 and above, the furnace functions after couple of efforts. Since last year it has to try few times before it stays on but if it is colder/cooler weather, it won't stay on at all. I get 10.5-10.6 at the fan continuously. Here are my questions/issues: I have read about regulator can freeze up even in cool temperature due to moisture in the tank and etc. Is this the regulator on the tank or is it the gas valve on the furnace? On the side note, when I try the stove on, I have notice steady blue flames. Is regulator/gas valve something that I can clean/service myself? I have read that some propane station can put Methanol in the tank to resolve this issue.

Second question, regarldess of my batteries been fully charged at 12.6 or higher, and regardless of having 12.6v at the cirvuite boar power feed wire, I get 10.5-10.6 at the fan when it kicks in? Is this normal? Is it suppose to be like this? I have cleaned and replaced any ground wires, including the chassis ones, that I could find.
At the end, the fact that the fan keeps going and the circuit board doesn't go to fail mode even after many tries, I am assuming this sould be propane issue rather than electrical/electronic issue. Is this a correct assumption?
Sorry about the long post. I appreciate any helpo that I can get.

Sounds to me like you have bad wire connection to the fan.  10.5v isn't enough to spin the fan at full speed, so the sail switch won't close and ignition will not be attempted.  I see nothing in what you described to suggest that gas supply is a problem.

You stated the furnace tries to kick in. Does that mean you see or hear the spark ignition, or just that the fan starts and runs. That's a key difference.  There is a programmed sequence of events that must occur for the furnace to light and continue running, so the point at which the process stops/fails is critical to diagnosing the problem. Throwing parts at the problem is expensive and rarely an effective way to fix things.  I've written an article on Furnace Troubleshooting that explains the process and the components involved. 


My article is in the RVForum Library at http://www.rvforum.net/miscfiles/Furnace_Trouble-2.pdf

Thank you.
The furnace/ignitor starts, you can hear the sound of the it, it (flame) may stay on for couple to few seconds and then the flame stops. The fan keeps going all the time. The fan never stops despites the ignitor/spark keeps trying to come on every now and then. My understanding is if there is a problem in the process of furnace functioning normally: fan comes on and reaches certain speed to create enough flow for sail switch to function and then ignitors ignites while the propane valve is opening and etc, the furnace/fan would stop trying after 3-4 attempts and the furnace, including the fan, would stop. In my case, the fan never stops and the system never stops trying to fire/spark. Also my understanding is that the fan needs minimum 10.5 to open up the sail switch. If that is the case at 10.5v, although I agree that I have too much voltage drop, the furnace should still function. Am I missing something?
Other confusion is why does it work in warmer temperature?

HRDWRK said:

Hi There:
I have this issue with our furnace for the past year that it doesn't come on all the time. The problem seems to be temperature related. In colder weather the heat doesn't come on despite the blower/fan keeps going. There is a chance that I might have two issues which I explain below. First thing to know if that  have replaced the sail switch, fail/safety switch twice with no change. I have also upgraded the circuit boar with Dinosaur brand last year. The problem has been that the fan keeps going, heat/furnace tries to kick in but most of the time it won't stay on despite the fan continues to operate. As I mentioned above, when the weather is warmer, 60-70 and above, the furnace functions after couple of efforts. Since last year it has to try few times before it stays on but if it is colder/cooler weather, it won't stay on at all. I get 10.5-10.6 at the fan continuously. Here are my questions/issues: I have read about regulator can freeze up even in cool temperature due to moisture in the tank and etc. Is this the regulator on the tank or is it the gas valve on the furnace? On the side note, when I try the stove on, I have notice steady blue flames. Is regulator/gas valve something that I can clean/service myself? I have read that some propane station can put Methanol in the tank to resolve this issue.

Second question, regarldess of my batteries been fully charged at 12.6 or higher, and regardless of having 12.6v at the cirvuite boar power feed wire, I get 10.5-10.6 at the fan when it kicks in? Is this normal? Is it suppose to be like this? I have cleaned and replaced any ground wires, including the chassis ones, that I could find.
At the end, the fact that the fan keeps going and the circuit board doesn't go to fail mode even after many tries, I am assuming this sould be propane issue rather than electrical/electronic issue. Is this a correct assumption?
Sorry about the long post. I appreciate any help that I can get.

Click to expand...

HRDWRK
When I had a similar problem with my Suberban furnace it was not a propane issue.....replacing BOTH the electronic control board AND the sail switch fixed it.

With that kind of voltage instead of the proper voltage level, probably about anything could happen that is abnormal.  First issue, in my opinion is find and repair the low voltage issue and take it from there.

^^^^^ X2 ^^^^^^^

The only temperature-dependent variable I can think of that is a "known" quantity is the vapor pressure in your propane tank which feeds the regulator.  Here are some numbers:  0 deg F = 24 psi; 30 deg F = 51 psi; 80 deg F = 128 psi; 90 deg F = 149 psi. 

Your water heater should be another "high flow rate" appliance.  If it works normally at the lower ambient temps, it is almost a certainty that there is something close to 11" WC at both the water heater's propane inlet and the furnace's propane inlet.  SOooooo ..... time to go to work with the voltmeter, I reckon.

Be sure to let all of us know the outcome.  Adds to the "problem fixes" knowledge base.

Good luck with the fix .......... know it's aggravating.

I'm NOT the expert, but is the thermocouple in the pilot light when it does light?  If not, the thermocouple will not sense the flame and shut the gas off.  Again, I would expect this to shut the unit down.

Okay, thanks guys.
I guess I will chase this voltage drop issue. I just don't understand why it is weather dependent. I guess I have to pull the unit out since I have checked and double checked what I can see and reach from outside unless there is another suggestion.

Temperature dependence can make sense if you realize that a battery is more efficient at warmer temperatures -- the chemical processes work better.

If I can make a suggestion, and this is dependant on how comfortable and confident you are doing electrical troubleshooting.  Start at the unit....where you have low voltage (10.5-10.6 volts) and work you way back towards the battery itself.  Take voltage readings wherever you can get a voltmeter on the leads/wires that are supplying the furnace.  When you find that at point x that the voltage is correct or normal, you will know that the problem is between there and the previous point that had the lower voltage readings.