From reading a bunch of on-point threads on this forum, I have learned that my Lennox 80 MFG goes into "watchguard mode" probably because it requires a control-ignition board and/or dual rod flame sensor upgrade, and that I'm at a point where I need to call in the pros do decide which. (I already tried cleaning off the flame sensor rods; didn't help.)
But I've found a recurring observation in people's description of the problem that's true for me too: It happens more in cold weather, and the system works fine in milder weather.
Seems to me the pattern should, theoretically, be the same in warm or cold weather; when activated, the system either works or doesn't. But if it's 40 degrees outside, my system runs fine -- full cycles every time the thermostat calls on it. When it's 10 degrees outside, it goes into watchguard mode all the time. Why would outside temp affect the communication between flame sensors and the board?
I don't plan to DIY this, it's just driving me crazy not knowing why the outside temperature matters. And it's not just simple odds, like "it happens more because the furnace is called on more"; this isn't a stats question, because it NEVER goes into watchguard mode when it's more than about 32 degrees outside. Why does this error occur more when it's colder?