Re: Furnace not Heating
Originally Posted by soxside
When the thermostat calls for heat this signals the electronic control module to turn on the induced draft blower for the exhaust.
The control module senses this is working properly it then turns on what looks like a small electric element ( in some furnaces ).
Once this element glows red the control module senses this is working properly it signals the gas valve to open to light the burners.
The burners will fire warming the heat exchanger to a predetermined temperature.
At this point the control module is looking at two sensors ( depending on furnace ) ....
1 - telling the control module the burners are fired and the gas is being burned .... otherwise if it doesn't see this correctly the control module will shut down the gas valve for safety .... since you don't want unburned gas hanging around.
2 - telling the control module the temperature inside the heat exchanger is warm enough.
It's at this point the blower is signaled to turn on and will remain running until signalled to turn off..
When the thermostat signals the control module to shut off the furnace..... the gas valve will shut off.
The blower should remain on removing the remaining heat from the heat exchanger until a sensor set to a predetermined low value shuts the blower off.
If your blower is coming on after the burners shut off ..... there is a problem.
There can be several issues causing the problem .... from a faulty control module .... faulty sensor(s) ... poor wire connection ... faulty gas valve .... faulty induced blower or negative pressure sensor .... blocked intake or exhaust .... etc..
it's difficult to pin point exactly the issue over the internet.
Considering this is a newly installed furnace the HVAC company that installed it should be coming back ASAP to fix it.
Hopefully this helps.
"" an ounce of perception -- a pound of obscure "