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Old 10-23-2020, 02:57 PM   #1
jvbutter01
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Dometic Furnace problmes

hello, I have a 2020 Passport with a dometic heater i dont see a model on it. I have read a few posts about purging and sail switches not working, other issues as well. Well its day 1 of 4 day trip, and the wind and rain kicked up. We turned heater on. Ran to town and I ran out of propane, it shut off. When we go back, I turned on new tank, running the stove now to bleed, running the propane water heater to purge the line, it fires up. the water heater is heating, i can hear it outside. I'm thinking the furnace heater should be purged.

Question:
does the furnace system detect NO FLAME and shut down the propane?

should I keep finance on to purge air, or for 2 min, then off, on for 2 min and off. Non knowing how long it will run before detecting NO FLAME and shut down.

thx
jim
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Old 10-23-2020, 03:11 PM   #2
LHaven
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What happens at that point depends on the layout of your rig. The main task of the purge is to fill the long feeder line with gas. In my rig, the range is just ahead of the furnace and the water heater is way aft. If both of those are working, only the short stub actually feeding the furnace itself needs a purge, and that is taken care of by the first ignition attempt. Now, if your furnace is distant from every other gas appliance in your rig, you may need two or three ignition attempts to purge the shunt, but this is something your furnace typically does automatically anyway by trying to start a few times before giving up.

The typical startup routine of a furnace is to turn on the fan, check for good airflow and no overheat, turn on the gas, try igniting it for 20 seconds or so, and if no ignition, turn off the gas, then the fan. Then typically it will wait some period (60 seconds?) and try again. It will do this two or three times, then give up. If you really have a difficult purge condition, you may have to turn the thermostat off furnace at that point, then turn it back on to begin the cycle again. If it still fails the second set of cycles, your problem is probably not purge.
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Old 10-23-2020, 03:25 PM   #3
jvbutter01
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Quote:
Originally Posted by LHaven View Post
What happens at that point depends on the layout of your rig.
LHaven,
thanks for the feedback. yes all depends on connection... seeing your post made me look again. so propane tank in front of 33ft trailer, about 15ft back is the stove connection 2ft past is the tap for the fridge (currently on elec.) and the furnace. when i open the furnace box i see both lines coming up. Previously i thought it was furnace and water heater. I was wrong, its furnace and fridge (running on elect so no purge help).

yea my heater never shut off... even after 5 min of running. so that is when i would start, run and shut off after after 3-5min. I was manually turning off at thermostat.

however it finally started heating. so were good. but this is still the question... how to purge, on and off, or on and let be
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Old 10-23-2020, 03:34 PM   #4
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Honestly, I have never had to purge because my tank ran out and I refilled it same day. I've had to purge when I shut my tank off in November and didn't turn it on again until March.

You should be able to valve your tanks shut, and not see the green in your indicator turn red for a couple days (assuming you turn off all the gas consuming devices). Anything faster than that, and you should be looking for leaks.

In your case, the furnace and WH may have been trying to pull gas, which would turn the indicator red, but still would leave low-pressure propane in the lines and not require a purge (air requires a purge).

If your heater runs for five minutes without really heating, it has a problem.
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Old 10-23-2020, 04:03 PM   #5
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Seems like there are different things to watch for in troubeshooting.


1. If starting with a new tank it just might take a while for the propane to get to the furnace

2. If the furnace blower just runs and runs but won't ignite then I would check the sail switch to see if it's gunked up with hair, etc. It could also be just faulty and need replacing. Also check the gas valve in so see if bugs have nested in there blocking propane flow

3. If the furnace is igniting/lighting and then turning back off then the sail switch is fine. It's either an igniter/flame sensor issue (distance from gas disperse screen or just not working) or a regulator issue (not enough pressure - more difficult to check and requires some special equipment).
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Old 10-23-2020, 06:14 PM   #6
chuckster57
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There isnít any purging of the gas line when the furnace starts. There are a couple of safety switches that prevent the gas valve from opening until conditions are met.
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