Check the heating command, 24 V controls and line-voltage load separately.
Electrical access and testing are for a qualified electrician. Isolate all involved circuits and verify they are de-energized before opening boxes, disconnecting conductors or measuring resistance. Energized voltage measurements require appropriate electrical safety precautions.
- Confirm the VisionPRO is configured for the installed heating system, set to Heat and requesting a temperature above the current reading.
- Check the integration kit’s demand indicator. The WarmlyYours diagram labels it as illuminated when calling for heat; it does not prove that current reaches the heater.
- Identify the exact RC840T-120 or RC840T-240. Check its incoming line supply, the 24 V control supply at R–C, thermostat demand at the control terminals, and its switched heater output using the matching diagram.
- If output is present but the heater remains cold, isolate and test the heating circuit against its factory label and installation records. If output is absent, distinguish missing supply, missing demand, wiring and relay faults before replacing a component.
The red, black and blue/white relay leads are line-voltage connections, not the 24 V transformer output. Do not apply household voltage to the thermostat’s R/C/W terminals. Keep ground-fault and required floor-temperature protection in place.
Sources: VisionPRO integration diagram, VisionPRO installation guide and RC840T installation guide.