Help Needed - Lennox Furnace going into Watchguard Mode


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Old 11-29-18, 08:29 AM
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Help Needed - Lennox Furnace going into Watchguard Mode

I have a Lennox G40UH gas furnace. It is about 10 years old.

I am experiencing an problem with my furnace. The furnace goes into Watchguard mode and I have tried cleaning the flame sensor. Infact i got the furnace service couple of months back as well. I have been experiencing this problem in last week or so. I also got the igniter replaced by HVAC guy and after that also it had issues. However what we found out is once we wiggle the gas valve wires after the igniter ignites it works. The HVAC guy mentioned to keep an eye on it and see if i have to keep doing it then we may need to replace the Gas valve. I want to make sure if that is what the problem is before i get it replaced.

Here is how it gets to the Watchguard mode:
1) Thermostat calls for heat
2) Combustion Air Inducer turns on
3) delay
4) gas valve opens and ignitor lights flame
5) flame stays light for a few seconds, then gas valve closes (no more flame)
6) delay
7) gas valve opens again and ignitor lights flame,
8) flame stays light for a few seconds, then gas valve closes (no more flame)
9)....this gas/ignitor sequence happens for a total of 4 or 5 trys before the furnance enters the Watchguard mode.

I then shut off the main switch and turn it back on. When the igniter ignites flame i wiggle the wires and all the burners start.

Can anyone help me troubleshoot this? I am really close to calling the hvac guy again who knows what they are doing, but i want to ensure if replacing the gas valve will resolve the problem. The thing that baffles me is why wiggling the wires turns the burners on.

I appreciate any feedback!
 
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Old 11-29-18, 12:39 PM
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What wires are you wiggling. If loose wires fix the problem why would you change the gas valve unless the terminals are the problem.

If the boiler starts every time you do this you seem to have located the problem just try improving the connections first.

Pics would be helpful if possible.

Just a thought, hope this helps a little.
 
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Old 11-29-18, 02:25 PM
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Thanks for the reply. Its the wires from the circuit board to Gas Valve. I will send a picture as well.
 
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Old 11-29-18, 05:53 PM
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Welcome to the forums.

Pictures definitely needed. We can tell you what to check.
Defective or poor solder on connections is a very common problem.
You need to know where to check to locate where the exact problem is.
How-to-insert-pictures
 
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Old 11-30-18, 08:06 AM
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Picture of furnace.

The wires i am referring to are the red and yellow wires.
 
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Old 11-30-18, 12:32 PM
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N,
If this happens again you can try jiggling the wires one at time to see if maybe you have a loose fitting connection.

Those spade connectors can sometimes fit loosely and do not make good contact with the terminals or the wires inserted into the spade connectors may be loose. I wouldn't jump into a gas valve just yet. It may just require a better wire connection.

Those spade connectors come in different sizes and if the wrong size connector was used it may have resulted in a sloppy fit and poor connection.
 
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Old 12-01-18, 12:32 AM
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Those on/off switches can also get dirty. Operate that a few times. In the picture you can see the dark lines on the terminals. That's where the connections slide on. You can spray a very small amount of contact cleaner.... even WD-40.... into the plug (not the valve) and then reconnect it to the valve a few times. That will clean that corrosion.

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Old 12-03-18, 06:42 AM
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Try out

Thanks guys will try out your suggestions..
 
 

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