No Heat

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Old 03-09-12, 04:42 AM
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No Heat

I have an American Standard Model#cdb100a945d3. Overnight it quit coming on. I have chked the code on the control bd and it is giving just 1 slow flash which indicates normal operation with no call for heat. The temp in the house is 64 and I have the thermostat set on 72. I have turned the t-stat all the way up & still no response. The thermostat is a Climate Technology digital thermostat. Is this a problem with the thermostat or where should I start looking?? Thanks
 
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Old 03-09-12, 08:20 AM
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Use a multimeter to check and see if you have 24 VAC at the R terminal and W terminal. The R terminal provides voltage going to the thermostat and the W terminal has voltage when the thermostat is calling for heat.

So if you have 24 VAC at the W terminal when the thermostat is turned up, you have an issue either with the thermostat or the wiring for the thermostat.

You can double check that by using a piece of wire to connect the R and W terminals directly, which should turn on the furnace. If it does, that confirms you have an issue with the thermostat or thermostat wiring.

Check that first.
 
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Old 03-09-12, 09:20 AM
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tried the jumper trick and heat came on. I will track it down from here as to whether it is the wiring or thermostat. Thanks so much
 
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Old 03-09-12, 10:46 AM
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Jumper R and W at the t-stat - if it comes on, the wiring is fine.
 
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Old 03-09-12, 11:00 AM
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The next thing I'd do would be to remove the thermostat from the base to expose the wires. Determine which wires go to the R and W contacts on the furnace and connect those with the wire. If the furnace comes on, you have a thermostat issue.


The wires can be bad. I recall one furnace that intermittently failed to operate. I eventually pulled new wire and discovered that rats had gnawed the old wires causing the intermittent failure to light the furnace.
 
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