Ducted Gas Heater Not Heating All Rooms? What's Going On

Why Your Ducted Heater Isn't Heating All Rooms

A ducted gas heater that warms some rooms well but barely heats others is one of the most common heating complaints we get at ATC Plumbing. In most cases, the problem isn't the heater unit itself — it's the distribution system. Here are the most common causes.

Zone Dampers Closed or Faulty

Most modern ducted systems use zone dampers — motorised flaps inside the ductwork that control airflow to different areas of the home. Check your zone controller first. If a zone shows as open but the room still isn't heating, the damper motor may have failed or the damper may be physically stuck. This requires a technician to inspect and fix.

Blocked or Closed Outlet Vents

It sounds obvious, but furniture placed directly over floor vents is one of the most common causes of cold rooms. Check that every vent in the affected room is fully open and unobstructed. Floor vents can also be manually adjusted — some have louvres that slide open and shut.

Duct Leaks or Disconnected Sections

In older Melbourne homes, flexible ductwork runs through subfloors and ceiling cavities. Over time, sections can pull away from outlet boxes or develop tears, dumping heated air into the ceiling or subfloor instead of the room. A licensed technician can inspect the duct run with a camera or by pressurising the system to find leaks.

Dirty Filter Restricting Airflow

A clogged return air filter forces the heat exchanger to overheat and may trigger the limit switch, reducing output across all zones. Check your return air filter — it's usually a slide-out panel at the return air grille — and clean or replace it if it's clogged with dust. This should be done every 3–6 months.

System Too Small for the Home

If the home has been extended since the heater was installed, the system may not have sufficient capacity for the additional floor area. A licensed technician can carry out a heat load assessment to determine whether an upgrade is required.

ATC Plumbing diagnoses and repairs ducted gas heating systems across Melbourne's south-east. Call 1300 282 758 to book a diagnosis.