Open High Limit on Goodman

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Old 01-03-10, 06:59 PM
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Open High Limit on Goodman

Hi,

New here and new to Home Owning in Chicago. As some of you may know it's pretty cold in Chicago right now. My furnace has been acting up and I hired a guy to come out and take a look. He replaced one sensor and a vaccum valve, but I'm still getting VERY short running times. The heating element will come on and the gas starts. After about 10 minutes or less, it shuts off the gas, the igniter turns on again but no gas. Fan seems to continue to run though. I noticed that sometimes the red LED flashes 4 times. On the label it states that means "open high limit". I'm getting heat to the 4th floor, some heat to the 3rd floor, and no heat to the 2nd or 1st floors. Could this be a matter of blocked registers? If so, can anyone recommend a proper HVAC guy that can completely clean the ducting? Is it possible that there is a damper in the system somewhere? Is it easy to locate the damper? Are they electric or mechanical?

Thanks
 
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Old 01-06-10, 03:57 AM
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Anyone? Please help. I've already spent almost $1000 and it's still not fixed.
 
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Old 01-06-10, 08:10 AM
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What was the sensor that was replaced?


Very likely, the reason the furnace is shutting off is because it's overheating and the high limit switch is shutting off the burners until the fan can get enough air past the heat exchanger to cool it off.

This is an elementary problem that any furnace repairman should have identified right away.

The usual problem is a plugged furnace filter, too many warm aie vents closed, having the return air vent(s) covered over, the air conditioning evaporator coil on the furnace plugged with debris or a defective fan motor or badly fouled and dirty fan wheel.

Check as many of those things as you can and see what you might find.

The basic problem is that not enough air is passing over the heat exchanger of the furnace, so it can't get rid of the heat being produced, causing the furnace to overheat.
 
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Old 01-06-10, 08:15 AM
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High limits usually trip due to lack of airflow. Do you have a clean air filter? Is the blower wheel clean? Does the motor seem to be running at full speed? Are the registers all open? The heater may have a bad heat exchanger too, so overall let a qualified technician come in if the obvious stuff doesn't fix it... Open registers and clean filter - blower. One more thing, do you have central a/c, you may have a dirt yevap coil casuing all this, but again usually it all comes back to lack of airflow.
 
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Old 01-07-10, 08:02 PM
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Thanks guys. This information will be helpful. The filter is clean and pretty new. How do I check to see if the coil is dirty? Does that involve me taking apart the furnace?

Model


Quick furnace shot


The sensor in the back of the picture is what the 1st service guy changed... I'm assuming the sensor in the front is the limit switch?
 

Last edited by spoonito; 01-07-10 at 08:32 PM.
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Old 01-07-10, 10:26 PM
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The 8:10 and 8:15 AM posts contain several likely causes of airflow restrictions and failures that commonly cause a furnace to overheat and shut off on the high limit switch.

You need to go through all of those thoroughly and methodically until you identify which is causing the problem.

Checking the filter and ignoring the rest of the list doesn't cut it if you want to solve this problem yourself.

If you don't want to do it yourself, you need to find an honest and competent repairman who can check these things for you and identify the problem.
 
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Old 01-08-10, 12:04 AM
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Thanks for the input, I would like to do the work myself I just don't know where the coil is located to check to see how clean/dirty it is. If it involves taking apart the furnace I would just need to know which parts need to come off so I can take a look.

Thanks.

Originally Posted by SeattlePioneer View Post
The 8:10 and 8:15 AM posts contain several likely causes of airflow restrictions and failures that commonly cause a furnace to overheat and shut off on the high limit switch.

You need to go through all of those thoroughly and methodically until you identify which is causing the problem.

Checking the filter and ignoring the rest of the list doesn't cut it if you want to solve this problem yourself.

If you don't want to do it yourself, you need to find an honest and competent repairman who can check these things for you and identify the problem.
 
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Old 01-08-10, 02:42 AM
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Couple more shots for you guys to help diagnose... I am no longer getter the 4 flashes (open high limit), but now it just stays on for about 10 min again and keeps trying to cycle on and off a few times then I get the single flash (max attempts exceeded). I read somewhere else that the burners may be pushing too much gas through as well causing heat build up... Don't know if I'm explaining that correctly.


Inducer fan (the small fan... don't know if that's what it's called) Looked clean to me and rotated freely


Main fan also looked clean


Sensor connect to main fan. I don't know how to check this one when the furnace is running as it's covered by a door and I think there's a door sensor that won't let the furnace run when the door is removed.


Radiator?




 
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Old 01-08-10, 06:18 PM
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Originally Posted by spoonito View Post
Hi,

New here and new to Home Owning in Chicago. As some of you may know it's pretty cold in Chicago right now. My furnace has been acting up and I hired a guy to come out and take a look. He replaced one sensor and a vaccum valve, but I'm still getting VERY short running times. The heating element will come on and the gas starts. After about 10 minutes or less, it shuts off the gas, the igniter turns on again but no gas. Fan seems to continue to run though. I noticed that sometimes the red LED flashes 4 times. On the label it states that means "open high limit". I'm getting heat to the 4th floor, some heat to the 3rd floor, and no heat to the 2nd or 1st floors. Could this be a matter of blocked registers? If so, can anyone recommend a proper HVAC guy that can completely clean the ducting? Is it possible that there is a damper in the system somewhere? Is it easy to locate the damper? Are they electric or mechanical?

Thanks
Why don't you contact that guy or his company, if the same problem persists? Did you pay the guy $1000 to replace parts that did not help?(And hopefully the $1000 was not just for changing out those parts!) And you are going to take that sitting down? If the furnace did not get fixed, get your $1000 (or maybe $900 of it)back. And tell him he can have his new parts back if he will put yours back in! Then start over from square 1, now knowing it is neither of those parts, but something else. Sounds like you got an incompetant furnace man. If the problem happens all the time, it should be easier to find the problem.

Any repair guy should be able to know if the high limit is shutting down. And if it is, if it is the switch itself shutting down earlier than it should (bad switch)?, or if the switch is doing it's job and shutting the furnace down because it is getting too hot. Ditto for the pressure switch.

And if it is getting too hot, to determine if one(or more) of these is it:

Too much gas/too big a flame.

Improper fuel-air mix/yellow flame - caused soot over time, and reduced inner area of exchangers. (Could also be blamed on poor venting of furnace - and if a different pressure switch was ever put in, someone may have sort of bypassed that problem if the new pressure switch is no longer as sensitive to a venting problem.)

Blower motor speed too slow.

Blower motor squirrel cage fins that are cupped are no longer cupped due to filled in with caked dust.

Secondary heat exchanger directly above the blower is partially plugged due to past filter changing neglect.

An ac coil above the furnace is clogged for same reason.

Too many duct dampers are closed. (And keep in mind if the air cannot get out the ducts with the least resistance, which would be the first and second floor, that it is harder for air to move through the furnace to only blow all the way up to the third and fourth floors.)

Cold air returns are blocked off.

Cold air or heat registers are caved in or partially filled with lots of dust/pet hair?, over the years.
 
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Old 01-09-10, 02:15 AM
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Fans look clean and can rotate by hand freely. I have closed some of the registers in order to get the air to flow to the 1st and 2nd floor (Furnace is on 3rd floor). Flames are blue, but I'm wondering if they are too strong/hot?

If there are any pics that you think you would want to see let me know and I'll try to get them uploaded ASAP.
 
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Old 01-09-10, 10:19 AM
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Is the flame sensor voltage supposed to jump up to 38 volts when the furnace is running? Also noticed a small chip in the porcelin base. Should this be a concern.
 
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Old 01-10-10, 10:36 AM
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Ok. I bought a new ignitor and flame sensor. Still getting the same thing. I double checked the dampers on the upper floors and adjusted them...
 
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