When a boiler loop keeps trapping air no matter how often it's bled, the culprit is usually the air separator that's supposed to be pulling those bubbles out for good.
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Quick answer
An air separator sits in a boiler's hydronic loop and continuously strips small air bubbles out of the circulating water so they can escape through an automatic air vent instead of collecting in radiators or baseboard heat. In a Langley home, a separator that's no longer doing this job effectively usually shows up as a circulator pump running noisier than usual, one or two zones that never fully clear after bleeding, or air returning within days of a full system purge.
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Even a properly sealed hydronic system takes on small amounts of dissolved air every time it's filled, topped up, or has a component serviced. Left alone, that air would circulate endlessly with the water, collecting in high points of the piping and inside radiators. The air separator's internal geometry is built to slow water flow just enough that trapped air rises out of it and escapes through an automatic vent mounted on top, rather than continuing to circulate.
A separator that's scaled internally, or whose air vent has failed, stops doing that job effectively, and the air simply keeps circulating instead of being removed.
| What you notice | What's likely happening |
|---|---|
| Circulator pump sounds noisier or rougher than normal | Air pockets in the loop are causing the pump to cavitate |
| A radiator or baseboard zone needs bleeding again within days | System-level air removal isn't keeping pace with new air entering the loop |
| Knocking or gurgling audible from pipes behind walls or in the mechanical room | Air moving through the loop instead of being separated out |
| Uneven heat across zones on the same loop | Air pockets sometimes settle unevenly depending on piping layout |
Before condemning the whole separator, a technician checks the automatic air vent mounted on top of it, since that small component fails more often than the separator body and is a much simpler fix. Mineral deposits can gum up the vent's internal float mechanism, preventing it from releasing air even though the separator underneath is still doing its job correctly.
If the separator's internal baffling itself is corroded or scaled enough that it can no longer slow water flow enough to release air, replacing the separator body is the more reliable path forward.
The relevant section of the boiler loop is isolated and drained, the old separator is removed from the supply piping, and the new unit is installed in the same orientation, generally paired with a fresh automatic air vent even if the old vent wasn't the primary problem. The full loop is then refilled and carefully purged of air before being put back into normal service.
A significant share of Langley's housing stock is newer construction from the past couple of decades, particularly through Willoughby, Walnut Grove, and Murrayville, much of it built with standard builder-grade hydronic components sized for cost rather than longevity. Those original air separators are now old enough in many of these homes that internal wear is starting to show, even though the rest of the boiler system may still be performing well. Out in the more rural, agricultural parts of the Township on well water, harder mineral content in the makeup water can also accelerate scale buildup inside a separator faster than it would on Metro Vancouver's municipal supply.
Safety note
Any work on the gas line, gas control valve, burner, pilot, or venting of a natural gas appliance must be done by a Technical Safety BC licensed gas fitter; CANRO holds gas licence LGA0043870 and boiler licence LBP0046450. If you smell gas, hear hissing near a fitting, or notice soot, a burnt smell, or a headache and nausea that eases once you're outside, leave the home first and call FortisBC's line at 1-800-663-9911 before doing anything else.
It removes small air bubbles from circulating water in a closed loop, routing them to an automatic air vent so they don't collect in radiators or cause pump noise.
If air keeps returning quickly, the separator or its air vent likely isn't removing air from the loop fast enough, so bleeding alone only treats the symptom temporarily.
Yes, the automatic air vent sits on top of the separator body and is a much more common failure point, so it's checked first before replacing the whole unit.
It can. Harder well water common in the Township's rural areas carries more dissolved minerals, which speeds up internal scale buildup compared with municipal supply.
It generally fits within a single visit once the loop section is isolated and drained, though system layout and access to the piping affect the exact time.
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