Boiler runs but does not provide enough heat to the home; radiators or baseboards are lukewarm.

Safety first: Turn off power before adjusting internal components. System water can be hot; use caution.

• Step 1 – Check thermostat and setpoint: Ensure the room thermostat is set above room temperature. On the boiler control, verify the heating setpoint is appropriate (often 160–180°F for baseboard systems, lower for radiant).
• Step 2 – Bleed air from system: Air pockets reduce heat transfer. Bleed radiators or baseboards starting with the highest floor. Use a radiator key or bleed screw and a container to catch water. Maintain system pressure during bleeding.
• Step 3 – Verify valve positions: Confirm all supply and return valves near the boiler and on main loops are fully open.
• Step 4 – Check circulator operation: With a call for heat, feel the circulator pump; it should vibrate slightly and the piping should gradually warm. If the pump is hot but pipes stay cool, the impeller may be damaged or the pump may be air-locked or failed.
• Step 5 – Evaluate system design (pro): If the boiler is undersized or the circulator is not matched to the system, a heating professional should perform a load and flow analysis.

Note: Gradual loss of heating capacity can also indicate scale buildup in the heat exchanger on some models.