Honeywell Large Dial Thermostat, T87N1026
You might notice that you get no heat or air, even though your thermostat clicks as it calls for heat. This clicking is a relay inside that closes to switch on the furnace. Now this no heat or air situation can happen for many reasons. Incorrect wiring, tripped circuit breakers, blown fuses, loss of gas supply, burned out heating elements, or a broken HVAC system could cause this. Here, we describe some of these causes, and then offer troubleshooting procedures and repair hints to resolve them.
Some of the tasks below are quite dangerous if you don’t know what you’re doing. So if you’re not at ease working with high voltages or natural gas / propane, then please hire the appropriate professionals to solve your heating problem for you.
If the heating problem happened when you installed a new thermostat, you may have erred in how you wired it. Perhaps you’ve reversed the W and Y wires. This would run the cooling stage though the thermostat is actually calling for heat. Other symptoms may arise too. These depend on which wires and how many of them you have connected to the wrong thermostat terminals.
Check for correct wiring at both ends of the thermostat cable. At the thermostat, attach all wires to the right terminals in the wall plate. Then, do the same at the furnace end. Get help from a professional heating system repairman if you feel insecure matching these wires up with the right terminals.
The solid copper wires in the thermostat cable can break if flexed too often. Or, perhaps the installer stapled the cable with too much pressure or stapler misalignment, and nicked the cable.
This issue normally shows up during new thermostat testing. But sometimes, it might not surface for years. Plus, settling of wall studs can flex these wires that installers often fasten to them. So, after decades, this flexing can wear wire coverings, causing faulty heat operation. In this case, the thermostat is still receiving power from the furnace, but the wires that it uses to call for heat are broken. So while the thermostat itself continues to operate, it is unable to communicate its heat requests to the furnace.
Replace the cable between the thermostat and furnace. Avoid tightly stapling the wire, and don’t fasten it more than you must for a secure installation. Lay it loosely.
Though the control relay in the thermostat might click to call for more heat, the relay itself may be worn out, its contacts no longer making a good connection when they close together.
When the thermostat clicks to turn heat on, the ignitor (could either be a spark type or hot metal variety) activates at the same time the gas does (in gas furnaces). But sometimes these devices burn out. Or, if your furnace has a pilot light, which is a small flame fed from the gas supply that is situated near the main burner. And this is what ignites main burner gas when the heat comes on. But if this flame goes out due to dirt or otherwise clogged piping, then you’ll get no main heating when the t-stat calls for it.
Though the furnace turns on, you may notice that the heating elements such as burners, electric coils, or heat pump compressor does not come on as well. This can happen due to a loss of electric power to said elements due to tripped circuit breakers, failed heating elements, broken relays, or a faulty control board. Or in the case of gas furnaces, it could be a loss of gas supply or faulty ignitor (the device that lights the gas coming out of the burner when the t-stat calls for heat, and again, faulty wiring or broken control board.
We saved this one for last, because it will likely be the most expensive repair. These bords typically run several hundreds of dollars, not to mention the labor costs you may incur to have a professional install them. Still though, they do go bad occasionally. And since these processors are what orchestrates the entire operation of the furnace, when they fail, the furnace often becomes non responsive to heat calls from the thermostat.
As should be clear, the thermostat-clicks-but-no-heat-or-air problem has many causes. Plus, most of them lie beyond the thermostat. But we hope that now, you know what might cause this. Why? Because knowing the causes of heat problems often helps in choosing the best fixes. Even though the right fix may cost the most, at least now, you have the data in front of you.
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