Furnace issue

[Sunflake]

Our new 2016 27BHS I think has an issue with the furnace. I'm a HVAC tech. When the furnace is running the burners shut off for a couple of minutes while the fan is still running. The T-stat isn't turning the furnace off because I turned it all the way up. It's almost like its tripping on high limit turning the burner off allowing the fan to cool the heat exchanger down and then turning the burner back on for a few minutes and then it repeats. Any ideas?

[abarkl]

All of our Atwood heaters in three RVs over the years have worked the exact same way.
We also have our home thermostats programmed to run 30 seconds after the cooling or heating cycle completes. Our thought was pushing the remaining cooled or heated air out of the venting system instead of wasting it.

[oldmanAZ]

I've never turned our T-stat all the way up. Normal operation for ours is the burners shut off at the T-stat set temp and the fan runs for a bit (I've never timed how long). That cycle repeats when the T-stat calls for heat again.

Your description of the system hitting a high-limit seems likely and a good thing, doesn't it? It seems reasonable to me that a RV furnace could have a lower high-limit than a home furnace.

How do you think the system should operate with the T-stat all the way up?

[hoppers4]

My furnace will cycle that same way. I'm fairly certain that the furnace is detecting an overtemp due to low flow. My furnace uses only two of the output connections (not sure if there's three or four on the furnace) and I think that's inadequate. I've never been too concerned about it as the rig will still heat up fine. It's just a bit slower getting there because of the cycling.

Adding another outlet vent somewhere would no doubt solve the problem.

[Sunflake]

Normal furnaces like in your home keep the burner lit until it reaches setpoint and then the t-stat turns the burner off allowing the fan to cool the heat exchanger down. This thing is cycling the burner below set point and the re lighting running a few minutes and cycling it off again. Just doesn't seem right. Almost like its not moving enough air across the heat exchanger.

[troutslayer]

Originally Posted by Sunflake

Our new 2016 27BHS I think has an issue with the furnace. I'm a HVAC tech. When the furnace is running the burners shut off for a couple of minutes while the fan is still running. The T-stat isn't turning the furnace off because I turned it all the way up. It's almost like its tripping on high limit turning the burner off allowing the fan to cool the heat exchanger down and then turning the burner back on for a few minutes and then it repeats. Any ideas?

I have the same issue. I just thought that was the way it was supposed to work. Then, there was a thread a couple years ago on this forum about this same topic. The general thinking was that there was a high limit being tripped due to the furnace ducting having too many bends or being crimped somehow. If this is true, I suppose it could be somewhat dangerous.

[Sunflake]

You certainly don't want to keep pushing the heat exchanger to the trip temperature. Our old 1990 Kit Sunchaser didn't do this. It ran like a normal furnace. I've got a warranty appointment this week so I'll let them know. I wonder if an email to Jayco could shed some light on this?

[hoppers4]

Be sure to let us know what the repair guy has to say.

[oldmanAZ]

Originally Posted by Sunflake

snip... The T-stat isn't turning the furnace off because I turned it all the way up. ...snip

But if you set the T-stat at, say, 75deg, does the T-stat turn the furnace off? Why are you setting the T-stat all the way up? Is this for a HVAC test you are conducting?

Just curious: How warm did your "... old 1990 Kit Sunchaser ..." get with the T-stat set up all the way?

The highest I've set our T-stat for is 72deg during the day. At night it is usually set for 62deg; 68deg if the grandkids are with us.

[Sunflake]

I had it originally turned it on to 70. The trailer was cold and had only been tuning a few minutes and the burner was cycling. So I wondered if maybe the battery was low so I tried again on Halloween while it was plugged in at our house and did the same thing. I turned it all the way up to make sure the tstat wasn't turning it off.

[oldmanAZ]

Originally Posted by Sunflake

I had it originally turned it on to 70. The trailer was cold and had only been tuning a few minutes and the burner was cycling. So I wondered if maybe the battery was low so I tried again on Halloween while it was plugged in at our house and did the same thing. I turned it all the way up to make sure the tstat wasn't turning it off.

GOT IT! Now I understand. Thank you.

[hoppers4]

Originally Posted by Sunflake

Normal furnaces like in your home keep the burner lit until it reaches setpoint and then the t-stat turns the burner off allowing the fan to cool the heat exchanger down. This thing is cycling the burner below set point and the re lighting running a few minutes and cycling it off again. Just doesn't seem right. Almost like its not moving enough air across the heat exchanger.

Your description fits the way mine operates to a tee. It can be 50 degrees in the rig, set the thermostat to 70 and the burner will cycle off several times on its way up to 70. I'm assuming it's overtemping several times due to low air flow from inadequate heating vents.

[Sunflake]

That's what I'm guessing the problem is as well.

[ALJO]

Be sure there's enough discharge openings if not install an extra one. And also the return air is not blocked. In most cases you need 4 discharge openings on a 25,000 BTU

[Sunflake]

I have 3 heat supplies on the floor and one small round one in the bathroom. When take it in will they add one because it's tripping? My underside is sealed.

[street rod 37]

What if you turn fan to on. See if the furnace still cycles. I agre e with you the limit is tripping

[Sunflake]

I'll double check tomorrow and make sure it's on high speed

[CharlieD]

I'm a ac/heating person also. I think the orifice size is too large for the air over the heat exchanger. Maybe with no duct there would be enough air flow across is to keep it from getting too hot and tripping the high limit, just a guess. I'm going to check the regulator on mine.

[CharlieD]

http://manuals.adventurerv.net/Atwoo...nuals-2007.pdf

[Sunflake]

What am I looking for in the instruction manuals? Did you find something Charlie?