Thermostat no power - Carrier Heating & Cooling

The Ruud furnace is probably compatible. Power stealing is a way to recharge the thermostat battery from the 24vac control voltage used to operate the furnace. If you install the Thermostat in the "separate power supply mode" it does not need to power steal ever and will be much more reliable. Some thermostats don't get enough power in the power steal mode to keep the battery reliably recharged, especially during the cold winter months because the poiwer available to "power steal" is highest when the furnace is NOT running. You will need a separate 24 vac transformer and some wire.

1 power wire (120v) will go to the thermostat and 1 power wire (120v) will go directly to the unit. The other wire on the unit will go to the other side of the thermostat. The safety precaution behind using a single pole to replace a double pole contactor is that you will always have 1 leg of power going to the unit. Many systems are designed like this from the factory, but it is always better to have a 2 pole to cut all power off to the unit unless it's in operation. The unit will still not work as long as it does not have both legs of power.
L1 to Thermostat T1 to Unit
L2 and T2 wired together.

This is only for 240v systems. 120v Will have 1 common and 1 power, therefore you will need to know which wire is which. Power to thermostat, common wired direct.

This model of Honeywell thermostat uses the 24v from the unit to power it. One of three things must have happened.

1. You have lost power to the furnace, therefore no power to thermostat.
2. You only have 4 wires hooked up on the thermostat and not 5. A lot of older homes had just 4 wire running to the thermostat, which will not work for this thermostat. You should have a wire connected to the (C) or (B) terminal on the thermostat, which ever one they have, I can't remember off hand. These are the Common terminals. They have to have the common from the furnace 24v power to operate.
3. Faulty thermostat, which will obviously have to be replaced.

Hope this helps and gets you to cooler days!

Most new digital thermostats are design to run with battery or A/C power, unless the A/C power is connected to the thermostat via a connection to the common "C" connection to the furnace common the thermostat defaults to battery operation and that is normal. Batterys last from 3 to 5 years in the average thermostat.

Try to open the electric iron and locate the thermostat . Secure the electric iron against any metal object that may cause electric shock or short circuit and plug it to a power source. Slowly adjust the temperature and using an electric tester check the power before the thermostat and after the thermostat. If there is a power before the thermostat and has no power after the thermostat then your problem is the thermostat replace it with a new one.

Most electric hot water heaters have two thermostats, one near the top of the tank and one near the bottom, and are covered by removable metal cover plates. The thermostats are pressed firmly against the bare metal wall of the hot water heaters tank.

The top thermostat usually has a high limit switch that will trip if the water gets too hot. When it trips it shuts off the electricity to both the upper and lower heating elements.

To reset the high limit switch there is usually a red button that you must press. When the upper limit switch trips it is often an indication that something else has gone wrong with the heater.

When the top of the tank is hot the upper thermostat removes power from the upper heating element and transfers the power to the lower thermostat and heating element. If the lower thermostat is defective, then the lower portion of the tank will not be heated and the supply will be greatly reduced.
Check for power at the upper thermostat terminals where the power is sent to the lower thermostat and heating element. If there is no power then the upper thermostat should be replaced. If there is power then check for power at the lower heating element. If there is no power at the lower heating element then replace the lower thermostat.
If there is power to the lower heating element then it should be getting hot. If it is not, replace it. Another possibility is a broken dip tube. Check for a broken dip tube and replace if necessary.

Hope this helps out

The cycling thermostat or the high-limit thermostat may not be the problem but rather the gas valve solenoid coils sitting on top of the gas valve assembly. Disconnect power then verify this condition by bypassing the thermostats. Refer to the image below and locate the thermostats.

Note: This is an image of an electric dryer but the thermostat and the thermal cut-off (cut-out) locations are the same.

Disconnect each of the thermostat wires then connect and insulate them properly. Once done, reconnect power and start the dryer. The gas valve solenoid coils are indeed faulty and both need to be replaced if the problem still persists. Click here for the procedure in replacing the solenoid coils.

Gas Valve Solenoid Coils Replacement Procedure

Either or both of the cycling thermostat and the high-limit thermostat are malfunctioning if the dryer continues to heat up with the thermostats bypassed. Disconnect power then reconnect the cycling thermostat wires but keeping the high-limit thermostat bypassed. Reconnect power then start the dryer. The high-limit thermostat is the culprit if the dryer continues to heat up. If not, then the cycling thermostat is the culprit.

Also do the other way; that is reconnecting the high-limit thermostat wires but keeping the cycling thermostat bypassed. The cycling thermostat is the culprit if the dryer continues to heat up. If not, then the high-limit thermostat is the culprit.

Replace the faulty thermostat and it should solve the problem.

Your thermostat should power on without a problem if it is battery operated, and even then, when you put batteries in it, it should still power up. Without knowing the exact model, the only other problem I can think of, the power to the thermostat is supplied by the furnace which is a common wire (usually blue) that is also hooked up to the C terminal on the thermostat. If there is a common wire hooked up, then you have to check if you have power to the furnace. If not, the problems could get more complicated. Hope this helps.

Thermostat may be bad and not suppling power to lower thermostat and element.

Sounds like Thermostat not working properly if no power there..

Do you have power to top element and power going into top of bottom thermostat if it has one.

If the thermostat is for just heat and is not a power robbing unit (used 24 volts to power a back lit display) all you need to do is hook one wire to R and one wire to W. If it is a power robbing unit you will need another wire that will connect to either C or B on the thermostat and to a transformer. If you can't run the extra wire from a transformer (supplying power) swap the thermostat to a unit that used a battery for the display.