Lennox G61MPVT stopped working.


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Old 09-02-13, 06:24 PM
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Lennox G61MPVT stopped working.

Hi guys. I'm a newbie here. I don't know the correct terminology to describe the various parts of my heater, but I am a qualified car mechanic, so have some tech skills. Here in Aus we don't get as cold as you guys. We see snow maybe 2 or 3 days in a year, but summer temps can be well over 100. Still, it gets cold enough to want heating in winter!
Yesterday our heating was fine, but after a brief power out the system has stopped working. It is a Lennox, model number according to the sticker isG61MPVT-60C-090-01. The stat is ComfortSense 3000 series, model 51M35.
Symptoms are; the small fan, I assume it's some sort of draught fan for ignition, is running, but ignition is not occurring. From reading this forum I discovered the LED diagnosis. Mine is flashing 2 then 3. The info on the door says that this means a blocked exhaust or inlet or condensate tube. I've tried to find anything blocked but nothing obvious seems to be. I'm not sure how far I can go before I need the "$175 before I look" man to come.
The system was installed in March 2007, and has been trouble free apart from a faulty SignatureStat a few years back.
Can anyone help?
 
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Old 09-02-13, 06:42 PM
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Look for a pressure switch near the induced draft fan. The switch will be about 3 to 3-1/2 inches in diameter. There will be a synthetic rubber hose from the switch to the housing of the draft fan. Remove that hose and make sure it is clear. Then, using a succession of sizes, run a drill bit through the hose nipple on the draft fan housing until you know it is clear. Replace the hose and try the furnace.

Post back if that doesn't work.
 
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Old 09-02-13, 07:03 PM
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Thanks, Furd. Under the house I go.
 
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Old 09-02-13, 07:46 PM
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Are these what you mean? There are 4 of them.
 
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Old 09-02-13, 08:02 PM
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All the hoses and nipples appear to be completely clear, although I did get a tiny bit of water out of the bottom one.
I forgot to say that the diagnosis chart says also Low pressure switch fail-open., so I guess you're on the right track. For testing purposes only, is it possible to bridge these switches? I assume they don't operate at mains voltage. (240v AC here)
 
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Old 09-02-13, 08:49 PM
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Ok. I decided to bridge the wires on the switches one by one. The last one I tried, the bottom left in the pic, fired the heater up, so I decided to pay a little more attention to the nipples. They still seemed clear, but the unit is working. Thank you Furd for your response. I think I know where to look now if it stops again.
 
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Old 09-02-13, 11:03 PM
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I've never seen one with four pressure switches. I hope that you only bridged the terminals for testing purposes and removed the bridge after testing. Those pressure switches are safety devices and bridging them defeats their purpose.
 
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Old 09-03-13, 06:18 PM
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The pressure switch may not be bad - there could be an underlying problem which is causing it not to close.

Don't run the furnace with a pressure switch bypassed; you're literally playing with fire.
 
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Old 09-03-13, 09:07 PM
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No, it was just an isolation exercise. I assume that I may have not cleaned the hose/nipple properly os something. A second try didn't seem to unblock anything, but it is working now.
 
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Old 09-03-13, 09:10 PM
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Thanks, Muggle. No, it was a bridge only for long enough to see the burners kick in. That showed me which switch to focus on.

I have already had a one house fire in my life, and that was more than enough.
 
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Old 09-03-13, 09:13 PM
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The four switches may be a local, as in Australia, requirement I suppose. It's like that here.
 
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Old 09-03-13, 10:21 PM
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I have a Lennox G60DFV that was installed in 2005. I received a free tune-up a year later as part of the installation package. A couple of months after the tune-up the furnace would not light, just sit with the induced draft fan running. I did some checking and found the corroded nipple I mentioned earlier. After cleaning it ran fine for another few months and then the same thing. This time rather than tear half the furnace apart I just ran the drill bit(s) down the nipple. It has been fine ever since.
 
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Old 09-11-13, 09:57 PM
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No such luck here. The furnace worked for a week and then stopped again. I bought a new switch and it's going fine again. Touch wood.
 
 

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