Question about Honeywell CT87B ROUND HEATING&COOLING MECHANICAL THERMOSTAT - WHITE Heater
Furnace runs thru a heat cycle then shuts down after cool down cycle, then restarts another cool down cycle and keeps doing this all the while flashing a green light 6 times for an error code of check power polarity
Posted by Anonymous on
You can make sure it is not the thermostat by crossing or jumping the R and W terminals (or associated wires) together. This will keep the furnace calling for heat. As it is approaching set temperature, get in front of the furnace and inspect the air filter to make sure it is clean, watch the control module for any error codes that may be turning off the system prematurely.
On a call for heat, the 24 volt thermostat sends a signal to the control module. The control module will indicate a call for heat with a light on the control either blinking or remain solid depending upon model. The inducer (exhaust) blower will purge all gasses from the furnace and pressurize a pressure switch. Once the pressure switch tells the module to continue, the electronic ignition will energize and send 120 volts to the igniter. The igniter will glow and you will be able to see it if viewed thru the small inspection port. Once the igniter gets hot enough, it sends a signal to the module opening up the gas valve (24 volts). Either a pilot will come on or the burner tube will ignite then spread the flame to all burners. Lastly a safety sensor will be looking for a certain temperature within a few seconds and the furnace will continue to operate and the room air blower will turn on in a minute or two.
What could go wrong? The unit will not run if there is no signal from the thermostat (bad thermostat or broken wire), the control module does not sense a signal from the thermostat (bad control), the inducer does not energize (bad motor), the pressure switch does not close (blocked vent piping, bad switch, plugged condensate hose), the igniter does not energize (bad control, bad igniter), the gas valve does not open or there is no gas (bad gas valve, broken wire, no gas), the pilot does not light (dirty pilot), the burner does not light (bad burner, plugged orifice, not enough combustion air), the flame does not spread to each burner (bad flame spreader, dirty flame spreader, more bad burners), the flame safety sensor does not detect flame (dirty or bad flame spreader, bad flame sensor, broken wire, bad control), or the room air blower does not energize (bad fan motor, bad control).
Posted on Mar 07, 2010
Does the flame and the blower cycle or just the blower...
if the flame is cycling then the flame sensor is dirty/bad.....or there is a bad ground....
if it is just the blower cycling then the gas pressure could be too low and the fire is not hot enough...the furnace also may do that if you are running fairly cool temps. in the house...
To check the gas pressure you need to have a tech. do it that has the proper equipment to read in. water column....to set the gas pressure for you...
Posted on Dec 30, 2010
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