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Old 11-13-2014, 02:20 PM   #1
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I need help with furnace, no heat ?

My furnace blower comes on but no heat, have just refilled propane and fridge is working on gas, I can hear thermostat 'clicking' but no heat,what should I check out first.
Thanks in advance
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Old 11-13-2014, 02:29 PM   #2
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Here are a couple of things I found at RVbasics.com



Fan doesn't run and no heat.

If the fan will not start you should first check that your battery is good and you have 12 volts at the furnace. You could have a tripped circuit breaker or blown fuse.
If the battery is good and you have electricity to the RV's heater next check the thermostat.
Remove cover and look for the "anticipator" adjustment. (Note: Some new thermostats do not have an anticipator.) It will be an adjustable control with a sliding contact over a straight bare wire or a bare wire wound about an insulating material. If the fan will not start set the temperature to maximum and then move the anticipator slider while listening for the fan to start. Be sure to wait long enough... it normally takes our furnace 30 seconds for the fan to start once the thermostat sends a signal.
If the fan starts after you move the slider then you have probably found the problem. In this case you may find a slider position near the original position that will work reliably. If your thermostat anticipator adjustment uses the straight wire design and the wire lies directly on the plastic housing then you should look to see if the wire has sunk into the plastic. This wire produces heat and causes the plastic to melt a little and the wire to sink into the plastic so the slider no longer makes contact. It may be necessary to replace the thermostat.
Fan runs but no heat.

If your furnace fan starts you can assume that the thermostat is working.
Possible problems are insufficient air flow through the furnace a bad propane valve at the furnace or a bad regulator at the propane tank.
A furnace contains an internal sail switch, that senses the air flow. If the air flow is not sufficient then the switch will prevent the furnace from igniting and the fan will run but you will get no heat. A slow motor speed could be caused by a low battery or other low voltage cause such as a bad connection in the wiring.
Low air flow could also be caused by a restriction in the ventilation system. Check to see if any heat registers are closed or blocked. Some furnaces will not tolerate even a partial closure of a heat register. .
If you have an electronic ignition check to see if the two contacts are touching or are too far apart. They should be about 1/8 apart.
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Old 11-13-2014, 02:32 PM   #3
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What type of furnace? Year? The clicking is usually the DSI attempting to light. My guess is the gas valve isn't opening for some reason. Does the external blower come on? Do you feel air exiting the outside flue? If there is no air exiting then the gas valve won't open.
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Old 11-13-2014, 07:25 PM   #4
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The furnace is a Hydro flame, Excalibur 8500-111 series, 1995, the clicking i hear is in the thermostat not the furnace, the fan seems to have plenty of air flow just no heat.
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Old 11-13-2014, 07:27 PM   #5
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Should I be able to hear the ignigter trying to light the gas ?
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Old 11-13-2014, 11:47 PM   #6
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Should I be able to hear the ignigter trying to light the gas ?
Yes you should hear the buzzing or clicking noise from the DSI attempting to light the burner. That said if it is a 1995 model that quite old. It is more likely that something just failed on the unit.
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Old 11-14-2014, 01:26 AM   #7
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If your furnace was working just prior to refilling your gas bottles. I have had this problem where there was still fresh air in the gas line to the furnace but the stove was working and The fridge even started working on gas. After several attempts at cycling the furnace off letting it attempt a start and turning it off again and then repeating this process it finally got the air out of the lines and lit when it got gas to it. In my old MH it would usually lite after two attempts. In my Montana 5th wheel I just purchased and had been sitting for a couple of years it took me about 6 or 7 attempts after the stove and fridge were working on gas. Once it started working, you could turn the system off and back to on and it worked fine every time because gas was in the line.
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Old 11-14-2014, 05:30 AM   #8
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Try lighting the stove. ...could be air in the lines...
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Old 11-14-2014, 08:19 AM   #9
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When the T-Stat calls for heat the control board starts the blower (1)
The blower blows closing the sail switch (2)
The control board then opens the gas valve (3) and begins sparking (4.1)
Gas Flows (5) And ignitets (4.2)
The flame heats the flame sensor (5)
The flame sensor sends .480 volts to the control board (6)
which then detects the .480 and continues operation (*)
When the T-stat says "Enough already" (RV is now warm)
The control board shuts off the gas flow (*)
and then turns off the blower after a cool down (*)

*: At nearly every step the control board is involved. IF IT IS BAD, things will not work.. I recommend replacement boards from Dinosaur boards.. When Mine went out the Dino board was less than half the price and when opened the box the quality of construction and workmanship, and then design was very clear to my trained eyes.

1: No 12 volt to furnace, blower motor shot
2: Low 12 volt, air ducts clogged, blower "obstructed" bad sail switch
3: Bad solenoid, Clogged Gas Jet
4: .1: Bad ignition circuit (high voltage) on control board. .2: Points too wide (Very common it seems)
5: These do not often fail but they can
5: Bad connection, NOTE:
5 and * Bad wire.

* applies to all steps by the way So does bad wire/connection.
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Old 11-14-2014, 09:40 AM   #10
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Quote:
Originally Posted by wa8yxm View Post
When the T-Stat calls for heat the control board starts the blower (1)
The blower blows closing the sail switch (2)
The control board then opens the gas valve (3) and begins sparking (4.1)
Gas Flows (5) And ignitets (4.2)
The flame heats the flame sensor (5)
The flame sensor sends .480 volts to the control board (6)
which then detects the .480 and continues operation (*)
When the T-stat says "Enough already" (RV is now warm)
The control board shuts off the gas flow (*)
and then turns off the blower after a cool down (*)

*: At nearly every step the control board is involved. IF IT IS BAD, things will not work.. I recommend replacement boards from Dinosaur boards.. When Mine went out the Dino board was less than half the price and when opened the box the quality of construction and workmanship, and then design was very clear to my trained eyes.

1: No 12 volt to furnace, blower motor shot
2: Low 12 volt, air ducts clogged, blower "obstructed" bad sail switch
3: Bad solenoid, Clogged Gas Jet
4: .1: Bad ignition circuit (high voltage) on control board. .2: Points too wide (Very common it seems)
5: These do not often fail but they can
5: Bad connection, NOTE:
5 and * Bad wire.

* applies to all steps by the way So does bad wire/connection.
This is the best most concise explanation of a propane furnace operation I have ever seen!
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Old 11-14-2014, 09:55 AM   #11
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try turning off thermostat wait 10 seconds and turn it back on
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Old 11-14-2014, 10:14 AM   #12
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I need help with furnace, no heat ?

Your furnace probably has a gas shut off valve right on the thermal coupler that was turned off when it was winterized. Turn your thermostat off. Take the cover to your furnace off inside the RV. Locate the fuel line on the furnace by the little site window that allows you to see the gas flames inside. on the bottom of the thermal couple you'll probably find a shut off valve. Turn it to the right away from the off position, and try again. If as you say you just refilled the propane there could be air trapped in the line. So let it sit for 5 minutes to get the air out of the line and then retry. Also check that there is not any loose electrical connections to the furnace.


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Old 11-16-2014, 12:19 PM   #13
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Hey BUKIMAN did you find a fix for your furnace? By the way wa8yxm I'm keeping your post for future troubleshooting, good stuff. Is there a message behind wa8yxm or just a handle.
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Old 11-17-2014, 06:49 AM   #14
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No, no fix yet, guess I'll have to take it in to a service dept and have it checked out.
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