need help troubleshooting furnace
This is a Tempstar NDLK075 efficient furnace I installed in ’91 in my shop. I haven’t had much trouble with it until this winter. I had the exhaust blower replaced by a furnace guy and it’s worked now about 6 weeks since that. This is what it is doing today: The blower is running all the time. The ignition isn’t glowing. It checks ok (has resistance). There is no line voltage coming to the ignitor. I unplugged the two prong plug from the module (where the module decides to send power on to the ignitor) and tested it for continuity. The light came on indicating the ignitor is supposed to light but the module didn’t make continuity. So, not to insult, but sometimes I don’t make it clear – it looks like the module is not sending power on to the ignitor when it says it is and it is supposed to. Is it reasonable to assume it’s the control module or am I overlooking something? (I checked and there is gas on my side of the regulator) I’m interested in troubleshooting this myself because last time the exhaust blower cost 400 and I found it on Ebay later for 100. In this case I find a range of control modules. The one I need ranges from 82$ to 186 online. I’m going to attach a schematic. Thanks if anyone is interested I’ll appreciate it but mainly because it’s free, sorry I’m not feeling too free and easy at the moment.
Replies
Note from the schematic that there is a pressure switch that must be happy before the burner can light. It could be upset because the exhaust blower isn't running, or because there's too much back pressure, indicating an obstruction in the flue pipe.
Thanks, I didn't notice that.
Thanks, I didn't notice that. I can check that out today. Fortunately the temp is above freezing so it's not an emergency yet.
Thanks for mentioning that pressure switch. Unfortunately it WAS happy.
There are costs that any business must bear and pass on to customers in order to stay in business.... and make a profit.
Some places do take that as far as they can, and then a little more while providing the customer with less.
The $100 special on eBay could have been a made in China knockoff.
Odds are the part supplied by the repair tech was OEM.
If there were problems with the part replaced by the service tech, I bet he/she would have come out and fixed it under warranty for maybe a year.
Lots of luck getting eBay to do that...
There are other things that a professional service tech should look at while making a repair. A person that fixes that stuff for a living would be aware of issues that a homeowner looking to save a buck will miss. That statement is true of many trade professions.
Because a furnace deals with fuel, electricity and can release things like carbon monoxide into the conditioned space if it is not functioning properly, I would suggest calling a pro.
Right - I was wrong to whine about that and could apply that to my own work as well thanks. In fact I just broke an Ebay ignitor trying to reshape it to what it was supposed to be to mount, so point well taken. I'm happy with the furnace repair and will probably be getting the same guy over to fix this. I did want to understand and fix it if I could, but it was unnecessary to put it that way.
Um, I thought my response was pretty well worded and professional.
I could have made it a lot shorter :)
Looking at it through my monitor, I know what the problem is.
If I told you, would you still call a professional... or just do the suggested repair?
What if the guesses offered here were wrong, and you wasted money on new parts that didn't fix the problem?
I have seen many situations where death for the occupants was a real possibility. Blocked flues and cracked heat exchangers can do that.
The guy replacing an ignitor or a assuming it is a board, and fixing the obvious problem, would never look for something else.
Ah, spoken like a true hvac-talk afficianado or moderator
Nope. Just seen some scary stuff.
quote
>> .>>The guy replacing an ignitor or a assuming it is a board, and fixing the obvious problem, would never look for something else.
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Submitted by junkhound on Sun, 01/17/2010 - 20:44.
Ah, spoken like a true hvac-talk afficianado or moderator
end quote
Or a home inspector I, er, heard about who years ago spotted one problem with a component and stopped looking.... .
It's fixed. Thanks for the
It's fixed. Thanks for the shots at it. It was the control module. There was no reset button on this furnace (odd for a reverse flow?). I don't know if this contributed, but the condensation tube got plugged and the condensation pump needed to be serviced. Sometimes I was told that pops a reset button close to the blower resulting in the control module not sending power to the ignitor. But in this case, all the sensors were happy. The 19 year old module was at fault. The new module I put in was for LP which meant it has a longer heat up period - the old was for natural gas. It worked, but maybe this will work better. There is a universal control module for this furnace a White Rogers 50347-843 hot surface ignition control.
I installed this furnace in '91 and it's worked great, have changed ignitors and done some other things. It makes sense though I think to not get to thinking you know a lot on any of this stuff - then you are destined for soon trouble. Plus I wouldn't knowingly call a repairman with that attitude.