Boiler displays TSTAT or Thermostat Error; boiler does not respond to room thermostat.

Safety first: This is a low-voltage circuit, but turn off power before changing wiring.

• Check thermostat settings: Ensure the thermostat is set to heat mode and the setpoint is above room temperature.
• Inspect wiring at boiler: At the Laars control, verify that the thermostat wires are connected to the correct terminals (e.g., T-T or R-W). Tighten any loose screws.
• Bypass test (advanced): With power off, temporarily connect a jumper between the thermostat terminals at the boiler. Restore power; if the boiler starts, the thermostat or its wiring is likely faulty.
• Replace batteries: If the thermostat is battery-powered, replace batteries and retest.

When to call a professional: If wiring is complex (multiple zones, controls), a technician should trace and correct the control wiring.