The power to the thermostat comes from the transformer in the furnace or air handler whichever you have. 1) the power to the furnace/AH is off, 2) the control fuse that protects the transformer is blown, 3) the transformer is defective, 4) the wire between the furnace and the thermostat got cut.
when running the heat-pump the air blowing from the heat ducts is not hot ( it's to cold for the heat-pump). you have a main furnace and it won't turn on ( is thermostat selected for this source), ( is the power switch for main furnace on ), ( is fuse for this furnace good). If these are good (check thermostat wiring at thermostat, and transformer).
Replace Thermostat
Try replacing your thermostat.
Bad Thermostat
A thermostat, as used in a motor vehicle, is essentially a heat actuated valve which, when open, allows coolant to cycle through the cooling system. The coolant absorbs heat from the engine and cycles it to the radiator, where the heat is exchanged to the ambient air which flows through the radiator fins. Air conditioning actually works in a similar manner, but is not affected by the thermostat - the thermostat does, however, allow you to have heat in your vehicle.
The thermostat turns on the fan to circulate air in the room, but it may not turn on the heat because the temperature setting has not been reached yet.
An ouside air temp changeover thermostat. lc
Yes, a faulty thermostat can cause the heating system to blow cold air. If the thermostat is not functioning properly, it may not signal the furnace to turn on and produce warm air. It's important to have a professional inspect and replace the thermostat if needed to ensure proper heating.
yes it can but everytime you want heat you have to put it on Emergency Heat..
A thermal power plant is more efficient when energy can be captured for reuse. Air coming into the combustion are ignites the fuel more efficiently when it is hot. Air leaving the combustion area looses some of its heat to the steam system, but a significant portion of the energy is lost with the exhaust gases. The preheater takes these two energy conditions (one area needing heat and one having "lost" heat) and combines them in a heat exchanger (preheater) where the heat from the exhaust gases is used to warm the incoming combustion air.
The furnace or air handling unit in the house.
Probably a bad thermostat.