just installed a honeywell t9 and the heat won't turn on, house is cold

Diagnosis

This issue typically stems from one of three root causes: a wiring mismatch during the installation of the RCHT9610WFSW2003, a tripped safety switch at the furnace, or an incorrect system configuration in the T9 software. Because the T9 requires a constant 24VAC power source via the C-wire to maintain its Wi-Fi connection and backlit display, the screen may be powered on even if the heating circuit is broken. This creates a "false positive" where the thermostat looks functional, but the signal to the furnace is never delivered. To confirm the root cause, look at the T9 display. If the screen shows "Heating" or a flame icon but the furnace doesn't fire, the problem is downstream (wiring or furnace hardware). If the thermostat is not calling for heat despite the set point being higher than the room temperature, the issue is a configuration error. Finally, if you hear a "click" from the thermostat but no action from the HVAC, check for a blown 3-amp or 5-amp fuse on the furnace control board, which often happens if the R and W wires touched during installation.

How to Fix It

Follow these steps in precise order to isolate and resolve the connection failure:

1. Verify Software Call: Press Menu > System Mode. Ensure it is set to Heat. Increase the set temperature to at least 5 degrees above the current room temperature. Confirm the screen explicitly says "Heating."
2. Inspect the C-Wire Connection: Remove the T9 faceplate from the wallplate. Ensure the blue (or designated C) wire is firmly seated in the C terminal and the red wire is in the R terminal. Give each wire a gentle tug to ensure the spring clamps have gripped the copper, not the plastic insulation.
3. Check the Furnace Door Switch: The T9 will not trigger heat if the furnace blower door is slightly ajar. Most furnaces have a kill-switch (a small plunger button) that must be fully depressed by the metal panel. Ensure the panel is screwed in tight; if it is loose, the furnace will have power to the thermostat but will not engage the burners.
4. Validate the R-Wire Jumper: If your system has a separate RC and RH terminal, ensure you are using the provided jumper or that the wire is in the correct terminal for your specific heat pump or conventional furnace setup. For most standard gas/electric furnaces, the power wire must be in RH.
5. Cycle the Breaker: Switch the HVAC circuit breaker to OFF for 30 seconds, then flip it back to ON. This resets the control board and clears any temporary lockout codes caused by installation surges.

If That Didn't Work

• Test for a Blown Fuse: Open the furnace cabinet and locate the control board. Look for a small automotive-style blade fuse (usually 3A or 5A). If the filament inside is broken, the thermostat will have power from the transformer, but the furnace will not respond to the "call for heat" signal. Replace it with an identical amperage fuse.
• Perform a Manual Jumper Test: To determine if the problem is the T9 or the furnace, remove the thermostat and use a jumper wire to momentarily connect the R and W terminals. If the heat kicks on immediately, the furnace is fine and the T9 is either configured incorrectly or has a defective relay.
• Verify Equipment Setup: Go to Menu > Advanced Setup > Equipment. Ensure the system is set to "Conventional" if you have a furnace/AC, or "Heat Pump" if you have a heat pump. If a conventional system is mistakenly set as a heat pump, the T9 will send the signal to the wrong wire (O/B instead of W), and the heat will never engage.
• Check the Condensate Overflow Switch: If your system has a secondary drain pan or a condensate pump, check if the pan is full of water. Many systems have a float switch that cuts power to the 24V "W" circuit to prevent flooding, which prevents the heat from turning on regardless of thermostat settings.

Heads Up

• Avoid "Wire Stripping" Overkill: Ensure only 1/4 inch of bare copper is exposed. If too much copper is exposed, it can arc or short against adjacent terminals, blowing the furnace fuse.
• C-Wire Necessity: Never attempt to power the T9 using only R and W wires; this model requires a C-wire for stable operation. Using a "power extender kit" is the only acceptable alternative if a C-wire is missing from your wall.
• Avoid Rapid Cycling: Do not rapidly change the temperature up and down to "test" the system. This can trigger the furnace's internal short-cycle protection, locking the system out for 5-10 minutes.