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“C” wire boiler side termination location (L7224C)

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Old 11-20-20, 03:03 PM
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“C” wire boiler side termination location (L7224C)

Hi, in a Honeywell control box, could someone point to the recommended “C” wire spot? I’m installing a new thermostat and have an obvious 2 wire system. Ty in advance.
 
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Old 11-20-20, 04:12 PM
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They don't advertise this but looks like the 2 terminal is C. The shared 3 and T terminal is R while the end T is W.
 
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Old 11-20-20, 05:37 PM
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Ty

Ty it makes sense. Should be ok as long as 24v @ #2 right? It’s just for power
 
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Old 11-20-20, 06:20 PM
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the "R" to the thermostat should make 24V with the common, "C". That will power your stat. Unfortunately, they typically don't advertise a 24V "C" terminal on the aquastat because they aren't designed to power other equipment like that. the easiest way to find the common on the aqua stat is by looking at the circuit board tracing on the back side (not so easy to view, though). specifically, the traces coming off on the built-in transformer.

One concern is the rating for the transformer built into that aquastat. I am not sure what the VA (the load it can handle to power equipment) typically is on an aquastat, but adding any additional devices that need power (ie your new thermostat) that it wasn't designed to handle, you always risks overloading and killing the transformer. which kills the aquastat ($200+). Your alternative option is to add an isolation relay and an independent transformer. Not hard to do but it requires a bit of thought and some electrical no how.
 
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Old 11-20-20, 06:21 PM
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Checked voltages

Lug: 1-20.4v. 2. 30.4v. 3. 8.9v 4. 0v
 
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Old 11-20-20, 06:35 PM
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Aqua stat schematic

This is my model diagram below. It shows a 24v thermostat top right. It shows “T T”. In the actual pic I posted above, to me it shows lug 3/4 as T T. But, lug 1. Has 20v, lug 2 30v, lug 3. 8v, lug 4 0v.

 

Last edited by PJmax; 11-21-20 at 06:12 PM. Reason: cropped/enhanced diagrams
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Old 11-21-20, 06:23 PM
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Use the info in the following thread for help...........
wiring-new-honeywell-thermostat-honeywell-aquastat-controller.
 
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