Boiler runs but radiators or in-floor heating remain lukewarm or cold.

Safety: Turn off power before working on pumps or zone valves.

• Check thermostat and setpoints: Confirm thermostats are calling for heat and the boiler's CH setpoint and outdoor reset curve are set appropriately.
• Bleed air: Bleed air from radiators, manifolds, and high points in the system.
• Verify zone operation: Feel the piping on each zone. If one zone is cold, its circulator or zone valve may not be operating. Listen for pump noise or valve motor movement.
• Check mixing valves: If using a mixing valve for low-temperature radiant, ensure it is not stuck in a low position.

If heat remains inadequate, a technician should check flow rates, pump sizing, and boiler modulation settings.