Boiler runs but radiators are hot only at the top or only some zones heat properly.

Safety first: Allow system to cool before bleeding radiators.

• Bleed affected radiators: Use a radiator key or screwdriver to release air until water flows steadily.
• Check zone valves: Ensure each Laars-connected zone valve opens when its thermostat calls. Manually open suspect valves to test.
• Adjust balancing valves: If present, slightly open or close balancing valves to improve flow to cooler zones.

When to call a professional: Complex multi-zone balancing and pump sizing should be evaluated by a heating contractor.