My Furnace says to use this schematic, but it's not working


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Old 04-25-14, 07:25 AM
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My Furnace says to use this schematic, but it's not working

My LAARS millivolt furnace says to use this (see below) for clock thermostats -- like the Nest that I am trying to install. I hooked everything up as diagrammed below. This gives the Nest power, but when I switch the heat on, the relay begins buzzing and the heat is never switched.

I'd try the schematic from hvactechfw but I'd have to run a new wire through my wall from my basement, and I'm not having any luck with that -- my existing wire is somehow secured inside the wall, so I can't just pull it through with the new wire attached at the end.

So, do you guys think that there is anyway that this diagram below is accurate and should work?

That would be GREAT news, if I just needed to switch something around to make this function. And if I do need the C wire after all, does anyone have suggestions for how to get the new wire through my wall when the old one is secured inside?

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Thanks!


Mod note: taken from this thread:
http://www.doityourself.com/forum/th...ansformer.html
 

Last edited by Shadeladie; 04-25-14 at 07:44 AM.
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Old 04-25-14, 07:46 AM
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Temp

Welcome to the forums.

The nest has problems when it comes to stealing power from a circuit. That's why we recommend you connect the C wire to the nest. You could try different relays as each one will respond differently.

Old wiring is usually fastened in the wall when installed because it's required for inspection.
I can't see your wall to make a direct recommendation. Possibly a snake is needed ?
 
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Old 04-25-14, 07:50 AM
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Ok, thank you for your prompt response. Any idea why they'd recommend that wiring? Is it because regular clock thermostats CAN steal the power from the circuit?
 
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Old 04-25-14, 10:00 AM
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The older clock thermostats could provide reliable operation using power stealing. I wouldn't recommend it with a modern digital thermostat.

The Honeywell Prestige IAQ can function with 2 wires to the stat.

Honeywell also offers wireless thermostats.
 
 

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