[bvigg]

Steps I have taken to repair Goodman Model # GUI100-4
1. Discovered furnace at church was inoperative.
2. Checked Thermostat /OK
3. Checked 115VAC / OK
4. Checked 24V / OK
5. Followed 24v to Safety Thermocoupler. Thermocoupler was open.
6. Shorted Thermocoupler with wire. Furnace started up.
7. Replaced Safety Thermocoupler PN 1NT08L-1090. Furnaced worked for 5 minutes and shutdown.
8. New Safety Thermocoupler was open.

What is the next step(s) in troubleshooting.

Thanks

[acetc]

Thermocouple is not the name for what you describe, it is probably a limit switch, check for lack of air flow, such as dirty filter or fan not coming on, Good luck, Mike

[bvigg]

You are correct Mike, The correct name is limit switch. Fan checked out OK, Filter was dirty but did not solve the problem.

I noticed there was a lot of heat coming out of the open area before the limit switch kicked in. The heat was in the front where the wiring is (near the limit switch and other electronics and gas valve).

When the furnace turned off there was a lot of cold back draft coming from the flue. My pastor did say one of the "saints" rerouted the flue for aesthetic purposes over the weekend.

It was then my guess that the backdraft from the new routing of the flue was causing too much pressure for the heat and gases to overcome and escape. Empirically, I tested.
I disconnected the flue and sure enough the furnace operated without kicking off.

I now have to learn some thermodynamics and figure out why there is so much backdraft so I can remedy the real problem or else I will hook it up the old unsightly way.

If you want to know more, basically, 'my brother' brought the flue out of the basement by running it about 10 ft laterally and 3 ft up with 4 elbows then out and up another two ft on the outside. (It could have been done with two elbows.) The flue use to run across the basement, exposed, some 40 ft, ultimately ending in a chimney stack.

He also drilled some choke holes in the elbow outside. Seems to me that would cause a velocity of air to start running down the flue... hmm??

He did what he knew best. Now we have to go from 'thought best', 'to operating and right.

Thanks for the good answer. BTW My co-worker echoed your thoughts.

Thermocouple is not the name for what you discribe, it is probably a limit switch, check for lack of air flow, such as dirty filter or fan not coming on, Good luck, Mike

[acetc]

Obviously you have a vent problem, for every foot horizontally you should go three feet vertically and it does not sound like that is the case. The vent should also be double wall type "B" vent as well to keep the gases hot so that they will rise and not cool off and fall back into the furnace. Your furnace sounds like it has a gravity vent (no induced draft motor) This problem that you are having is very serious and should be corrected ASAP.
Good luck, Mike

[bvigg]

Mike,

From my studies, it looks like I have three choices...
1. Hook vent back up to original design, (functional but aesthetically not pleasing, cheapest)
2. Buy high effieciency furnace and revent directly outside.(meets code, highest non recurring cost $1100.00 but saves money over the long haul.)
3. Buy Power Vent to help induce drafting (just learned of these, cost not too bad $300.00, meets code but adds small recurring power cost, maybe a good short term solution)

Thanks for your concern. If you have any comments on Line Items 2 or 3 let me know.

Barry

[acetc]

A 90% furnace might be the best way to go if the money is not a problem. This type furnace will be the easiest to vent ,can be vented horizontally through the outside wall with PVC pipe and this will save money on your fuel bills. Mike

[hvac1000]

You are having a roll out problem. That is what is tripping the safety limit.
Code calls for a 1/4 inch per foot rise for the chimny connector.
I would also check your combustion air or lack there of.

If this system was working for years then somethig has changed and it seems the (saints) as you called them were up to no good. LOL . I would check there work over and you will probably find the problem.

[bvigg]

I temporarily rerouted it (see below). Well more than a 1/4" per foot. It worked fine that day... but... that was on a 55 degree day. The temperature plummeted to 38degrees and that exhaust flue was just as cold as the temperature outside. The same problem started again.

It doesn't seem that the exhaust can overcome the cold air in the exhaust pipe and it the heat backs up and wants to trip again.

^ <----only 5ft off ground
|
--------------------------___|-------------------Basement wall
/
/ < short pipe is 3 ft long w/45 degree rise
... /... Ground
/
________/ <-----Horizontal leg has a 30 degree rise and is about 8ft long
/
/ <----- short pipe is 3 ft long w/ 45 degree rise
__F_|_ <---- flue is cold upon start up, heat never overcomes cold pipe
|
|
|
|


I am going to reroute it to original configuration whichhas a run of about 40 feet inside the basement then into the chimney flue.

How does this sound...
Saints are nothing but sinnners (aints) who have been (s)aved by God.
(s) + aints = saints. Can't have a saint with the salvation given by God.
Once that is done we need to learn how to correct what is wrong by doing what's right.
Here we are.

You are having a roll out problem. That is what is tripping the safety limit.
Code calls for a 1/4 inch per foot rise for the chimny connector.
I would also check your combustion air or lack there of.

If this system was working for years then somethig has changed and it seems the (saints) as you called them were up to no good. LOL . I would check there work over and you will probably find the problem.

[bvigg]

I should have previewed the diagram, it did not show up correctly. Basically it was a furnace with a 3ft/45 degree angled run coming out of the flue toward the basement wall then 8ft 30 degree run parallel to the wall, then another 3ft/45 degree run up to the wall , then out the basement wall and up 5 ft.

[hvac1000]

40 feet inside the basement then into the chimney flue.

Way to long to get a 1/4 inch per foot rise. It looks like a major problem with the flue connector and chimney.