I have a Reznor unit heater UDAP. 45,000 BTU. I installed it after trading with another guy who bought it new and used it for a few months. It is tripping the high limit switch. The board blinks 3 times, indicating a rollout switch according to the manual. Rollout switch tests ok. put a temp sensor in by the high limit switch, it read 240F when it tripped the high limit switch which is a 220F. I also took the limit switch loose and ran it and it did not shut down until i did it manually. Heater is Vented horizontally, total distance of vent pipe is about 5 ft with a 45 degree bend 1 foot from the back of the heater. So it appears as though the heater is overheating, and the high limit switch is not bad. Vent fan and blower fan seem to be working well. Ideas on what could be causing it to get too hot?
Reznor unit heater tripping high limit switch
- Thread starter retrorock
- Start date
sms1974
Well-known member
do you have a combustion air make up? I've seen more than one of these units installed by a home owner who doesn't do a fresh air intake for combustion air. if your garage is pretty tight it will get to a point where the exhaust venter has exhausted the space in to a negative pressure. this effects the flow of gas and air through the heat exchanger and can cause it to overheat. open a door or window and see if the unit runs normally.
other possibilities could be gas pressure or your fan isn't moving enough air through the unit... some pictures would be helpful
other possibilities could be gas pressure or your fan isn't moving enough air through the unit... some pictures would be helpful
Ohmthis
Well-known member
Did you clean it up really well before you installed it. The blower, or any heat exchangers could be really dirty and not letting the proper airflow. X2 on gas pressure too, did you just connect it and run? Is it a NG or LP unit?
Ok first let me apologize for not posting all the info. I was in a bit of a hurry and forgot to post some of the info.
Unit is NG and very clean. Gas pressure has been checked and is set at 3.6 WC. I did run the unit with the walk in door open and there was no change. The fans seem to run fine, although i was a little surprised that the blower motor did not blow more air than it does. As near as i can tell it spins freely and does not make noise, just doesn't blow as hard as i thought it would. I will get some pics tonight and post them.
Unit is NG and very clean. Gas pressure has been checked and is set at 3.6 WC. I did run the unit with the walk in door open and there was no change. The fans seem to run fine, although i was a little surprised that the blower motor did not blow more air than it does. As near as i can tell it spins freely and does not make noise, just doesn't blow as hard as i thought it would. I will get some pics tonight and post them.
acmikee
Well-known member
is the fan running in the right direction.
what is the temp rise in and out
is the unit level, is the flu level or have a slight up bubble, can you feel air coming out of the flu
what is the temp rise in and out
is the unit level, is the flu level or have a slight up bubble, can you feel air coming out of the flu
Fan is running the right direction, blowing out the front of the unit. Unit is level, flue has a very slight rise. Air is coming out of the flue, seems to vent pretty well. I do not know the temp rise in and out. I will need to borrow the neighbors meat thermometer again to check that. I have a funeral tomorrow so it will take a bit to get that measurement.
roscoe2000
Well-known member
There should be a second temperature limit switch which would be set lower than the high limit. This second switch would turn the burner on an off depending on the heat exchanger temp. Your hi-limit is more of a safeguard, where as this second switch operates the burner. All of these are separate from the thermostat which initiates the call for heat.
Consult the wiring diagram on the inside of the panel which would layout out its control sequence.
Consult the wiring diagram on the inside of the panel which would layout out its control sequence.
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I will check the wiring diagram, but when I took the high limit switch out of the heat exchanger area, the unit did not shut off until I shut it down so I would think that would indicate that the unit was actually overheating. When I measured it, the temp next to the high limit switch go to 25 degrees over the high limit switch setting before it shut down.
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roscoe2000
Well-known member
Try to post a pic of the wiring diagram.
I found this information your High Limit is set for 220 deg F. Your "Flame Rollout Limit is 225 or 200 deg F with option AL2B".
I found this information your High Limit is set for 220 deg F. Your "Flame Rollout Limit is 225 or 200 deg F with option AL2B".
sms1974
Well-known member
you have either a gas pressure (to high), combustion ventor (not moving enough air, could also be venting) or heat exchanger issue...
what is your exhaust vent total length and what kind of cap is on it?
I would start with dropping your gas pressure down a little and see what happens, you said it was set at 3.6? was that done with a water manometer or a digital manometer? I ask because the digital ones are not always accurate, water doesn't lie..
what is your exhaust vent total length and what kind of cap is on it?
I would start with dropping your gas pressure down a little and see what happens, you said it was set at 3.6? was that done with a water manometer or a digital manometer? I ask because the digital ones are not always accurate, water doesn't lie..
acmikee
Well-known member
can you lower the unit 1" your flu looks like it doesn't have enough pitch
exhaust vent length is about 5 ft. I have a T shaped cap on it, Which i removed and ran unit, no change, still tripped limit switch. i honestly don't know if i will be able to lower the unit easily. i will need to take ta look at that. i will also check it to see what my rise is. I checked the gas pressure with a digital manometer. i will try to lower it a bit and see what happens. Perhaps to about 3.2 WC?
Pic of wiring harness attached, not sure that it is another switch though, as i said, when i took the high limit out of the heat exchanger area and ran the unit, it did not shut down until i shut it down fearing that it would overheat.
Pic of wiring harness attached, not sure that it is another switch though, as i said, when i took the high limit out of the heat exchanger area and ran the unit, it did not shut down until i shut it down fearing that it would overheat.
klassenl
Well-known member
Check and make sure the fan is running correctly. If it runs well with the limit switch out of the heat exchanger then the fan isn't moving enough air.
Ohmthis
Well-known member
Check and see which speed tap the motor is wired to. You want it to run on the high speed tap unless your heat rise doesn't fall into spec. Is it a capacitor run motor? You can check the capacitor and make sure it is in spec.
Ohmthis
Well-known member
with the venting motor (draft inducer) and a pressure switch I don't think it's the draft. You would shut down on a pressure switch fault if that was the case.
sms1974
Well-known member
these units have a single speed fan...
its possible the fan is not running up to speed...
sms1974
Well-known member
I've seen them pull enough negative pressure to make the switch close even with a birds nest in the flue, also with one cell of the heat exchanger restricted.
yep, checked to make sure, it is a single speed fan. Adjusted gas outlet pressure to 3.15 WC and it still tripped high limit. It is a capacitor run motor, not sure how to check that. Any way to check to see if fan is running up to speed? Anyone have one of these and can tell me of a way to guestimate if it is blowing as hard as normal? It does not seem to blow that hard, but i have nothing to compare it to.
I think i figured out a way to drop the heater itself about an inch to increase the rise of vent pipe. will try that next.
I think i figured out a way to drop the heater itself about an inch to increase the rise of vent pipe. will try that next.
theoldwizard1
Well-known member
If you are tripping the high temp limit switch you have one of two problems.
- The vent is not following enough volume.
- The main fan is not blowing enough cold air across the heat exchanger.
Disconnect the exhaust duct as a test (only) and see if high temp goes away. reconnect it.
What is the motor nameplate rpm of the fan? What should it be? Call mfr.
3.5"wc gas pressure seems very low, but not the cause of overheating. What is the operating gas pressure range specified by the mfr?
What is the motor nameplate rpm of the fan? What should it be? Call mfr.
3.5"wc gas pressure seems very low, but not the cause of overheating. What is the operating gas pressure range specified by the mfr?
sms1974
Well-known member
I was refferring to supply pressure to the unit, not output of the units regulator.
Typically ng supply pressures are 6-7 wc and could be as low as 5 and as high as 9"wc at the output of the utility regulator.
3.5 wc is the operating spec from the manufacturer, which is what i meaxured and set.i looked up the fan speed and it was i believe 1500 rpm, butihaveno way thT i am awafe of to check that. it has been a usy week so iam just now getti g back to this. i will lower theheater an inch and or heck to see if it runs cooler without the flue connected.
any ideas onhow to check the blowef fan to see if it is blowing hard enough? it just doesnt blow as hard as i expected.
any ideas onhow to check the blowef fan to see if it is blowing hard enough? it just doesnt blow as hard as i expected.
sms1974
Well-known member
check the amp draw of the motor, there will be a rating tag on the motor that will say what the amp draw should be. if its not at the rating i would suggest contacting Reznor. it may still be in warranty.
LS6 Tommy
Well-known member
I thought of that. The diagram shows a single speed motor. Next step is to check fan motor amperage.
Tommy
i dropped the unit 1 inch and no change. I will check amperage later tonight. I can check the orifice as well. i was eyeing that earlier today.
Other owner changed it out because he had a small garage, and someone told him it would short cycle and not be very efficient. So he trading me for a 30,000 Btu heater. He never said it tripped a limit switch though. I am willing to still give him the benefit of the doubt. After we traded, he texted me and said i made a good trade because the other heater was slow to heat up his garage.
Other owner changed it out because he had a small garage, and someone told him it would short cycle and not be very efficient. So he trading me for a 30,000 Btu heater. He never said it tripped a limit switch though. I am willing to still give him the benefit of the doubt. After we traded, he texted me and said i made a good trade because the other heater was slow to heat up his garage.
i finally got an opportunity to work on this again. I checked the tag on the motor and it said 1.2 amps. I checked the motor while running and got 1.12 amps. so that seems to be within the acceptable range. i guess my next step is to check the orifice size and try to pull the vent pipe off to test it without the vent.
D45
Well-known member
Did you ever get this fixed?
I have a "3 code flash" also
I have a "3 code flash" also
Hi all, I'm new here and this is my first post. I've had the same code come up and issues RetroRock and have never been able to solve them.
Has anybody figured this out yet?
I found this YouTube video and it ended being the blower fan (not the induction fan) was the wrong distance away from the motor, resulting in not enough air flow across the Hx.
Has anybody figured this out yet?
I found this YouTube video and it ended being the blower fan (not the induction fan) was the wrong distance away from the motor, resulting in not enough air flow across the Hx.
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D45
Well-known member
Yes I fixed mine no issues since
www.garagejournal.com
Hot Dawg 75K Fault Code
So, I went to turn my heater on this morning, just to make sure everything was good..........nope It turns on, fan blows, and no warm air I take off access panel and the LED has 3 flashes Any quick and easy ideas, that I can check myself?
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D45
Well-known member
Pinched and welded the seam
It's all in the link
It's all in the link
D45
Well-known member
To fix this problem, you will need to remove the top burner and pinch together its edges per the pictures below. Remove the burner side plate, than remove the two screws that hold the burner in place and pinch or hammer the top edge, just above the center hole to stop this extra gas path
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Well, the OP hasn't been around since 2017 so we will never know.
One question I had is what is the style of the termination cap. Some are too restrictive. Run it without the cap on the end of the exhaust and see what happens.
Jim greengo
Well-known member
Have you tried running it with door open and flue disconnected?
I have serviced many udap Reznors. Tripping the rollout switch if it is not overfiring, is caused by a partially blocked heat exchanger. If the unit has not been well maintained, annual cleaning of the heat exchanger inside and out, it will eventually trip the rollout switch. I also don't recommend pinching and welding the burner. That is a total hack job. There are already enough hacks in this industry, don't add to it.
I have seen quite a few Reznors with burned out heat exchangers. You need to look closely as the holes might be small. I had one tech got out on a call three times for a Reznor UDAP that would trip out, then the forth trip I went out. Climbed up a ladder and looked throught the fan gaurd and saw burned out spots.
D45
Well-known member
This issue is commonly found on brand new units.......