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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 8769
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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Was replacing my honeywell thermostats with 2 new wifi

Customer Question

was replacing my honeywell thermostats with 2 new wifi Honeywell thermostats
first one went great - got it online...
then when I installed the 2nd one - i blew something. the first thermostat now does not work. Replaced the 2nd one with my old one and still no power to either thermostats. No Circuit breakers are tripped. Went into Attic and saw a Honeywell HZ311 controller - it's LED's are not on. Not sure what I do next.
Submitted: 2 years ago.
Category: HVAC
Expert:  Phil replied 2 years ago.


You accidentally shorted some thermostat wiring because you probably did not turn off the power to the furnace when you changed the thermostats.

There is a 3 amp automotive type fuse in most of those cards that is likely blown, the printed circuit board is generally mounted on the furnace or air handler blower, and will have the thermostat wires run to it.

Look that over, and if replacing the fuse does not work, send me photo's of the printed circuit card showing the thermostat connections, and a clear well focused photo of the wiring diagram glued to the inside of blower door....

use the paper clip icon for that, its at the right end of the tool bar above.


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