Air in Your Heating System & Bleeding Radiators
Trapped air causes cold radiators, gurgling and poor circulation. Why air gets in, how bleeding helps, and when recurring air means a real fault.
Air in a heating system is one of the most common reasons a radiator goes cold at the top or gurgles. Bleeding a radiator to release that air is a task many homeowners can do — but recurring air is a symptom, not just an annoyance. This guide covers both the fix and what it might be telling you.
How air gets in
- Fresh water added during top-ups carries dissolved air.
- Corrosion in an untreated system slowly generates gas.
- A leak that draws air in as the system cools.
- Air separators or auto-vents not doing their job.
What bleeding does
Bleeding opens a small valve at the top of a radiator to let trapped air escape until water appears, restoring full circulation so the whole radiator heats. It is generally within reach for a careful homeowner, with the heating off and a cloth to catch drips — then re-check system pressure afterward.
When recurring air is a warning
If you bleed radiators and the air keeps coming back, something is generating or drawing it in — corrosion, a leak, or a circulation fault. That needs a technician, because the underlying issue (often poor water condition) also damages the boiler over time.
Key takeaways
- Trapped air causes cold-at-the-top radiators, gurgling and poor circulation.
- Bleeding is usually a safe homeowner task — heating off, then re-check pressure.
- Air that keeps returning signals corrosion, a leak or a fault that needs a technician.
Frequently asked questions
Why do my radiators keep needing bleeding?
Repeated air means it is being generated or drawn in — usually corrosion in untreated water, a small leak, or a circulation problem. Bleeding treats the symptom; the cause needs diagnosis to protect the boiler and radiators.
Is it safe to bleed my own radiators?
Generally yes, with the heating off and care to catch drips, then topping the system pressure back up. But if air returns quickly, or pressure will not hold, stop and call a technician rather than repeatedly bleeding.
Related on GasBoilers.ca
Explore more boiler guides
Boiler question we didn’t cover?
Our licensed, Red Seal–certified gas technicians serve all of Greater Vancouver. Upfront pricing, same-day service available.