Ducted system not heating
Same symptom but on a ducted system — read this if it's whole-home.
Help guide · No heat output
Heater on but blowing cold air? Burner's not firing.
You can hear the fan, you can feel air at the vents, but it's barely warmer than the room. The fan and the burner are two separate systems on a gas heater — and when the fan runs without the burner firing, you've got a fault that's almost always a same-visit fix. Here's how to narrow it down.
Same-day metro Adelaide
Most fixes under $300
Common parts in van
Upfront pricing
60–90 min on site
Full diagnostic
CO test included
What's happening
Fan and burner are independent systems
A gas heater has two main moving parts. The burner makes heat by burning gas across a metal heat exchanger. The fan moves room air across that hot heat exchanger and blows the now-warm air out the vents. In normal operation the burner fires first, the heat exchanger gets hot, then the fan kicks in 30–60 seconds later to push the warm air around.
If the fan runs but the air stays cold, one of three things has happened. (1) The burner never fired — the fan is just blowing room-temperature air. (2) The burner fired briefly then dropped out on a safety lockout, and the fan is in its post-purge cool-down. (3) The unit is in fan-only mode at the controller (more common than people think — it's an easy setting to bump).
The diagnosis is figuring out which of those it is. Most can be sorted with a quick check of the controller, the thermostat, and the filter before you even need to call us.
Safety check
Is this dangerous?
No. A heater blowing cold air is the safest "fault" you can have — the burner isn't running, so there's no combustion to go wrong. CO risk is essentially zero. You're just cold and annoyed.
The exception: if the heater is firing intermittently and you can smell gas, soot, or "burning electrical" at the vents, turn it off at the controller and the unit's isolator and ring us. If you can smell raw gas anywhere in the house, ring 1800 427 532 first.
Right now
What to check in the next 5 minutes
1
HEAT not FAN
Check the controller mode is HEAT (or AUTO HEAT) — not FAN-only. Easy setting to bump accidentally.
2
Setpoint above room temp
Set 5°C above current room temp. If it's lower, the heater is correctly not heating.
3
Check the filter
Pull the return-air filter (ducted) and check it's not choked. Blocked filter triggers overheat lockout.
Diagnosis
What's likely causing it
- Controller in fan-only mode (check this first). Common. The fan runs, no burner. Switch to HEAT mode. Free fix if that's all it is.
- Thermostat issue. Setpoint below room temp, dead batteries in a wireless thermostat, or failing contacts in an old wall thermostat. $180–$320 if it needs replacing.
- Ignition failure. Igniter or pilot won't light the burner — control board calls for heat, gas valve opens briefly, no flame, lockout, fan runs on cool-down. $110–$180 igniter or $45–$140 flame sensor clean.
- Gas valve stuck. Igniter sparks correctly but the valve isn't opening. $400–$650 fitted.
- Heat exchanger limit switch tripped. Past overheating has tripped a one-shot safety limit and locked out the burner. Fan runs to cool. Service required to reset and identify why it overheated.
- Control board fault. Last thing we check. $480–$950 fitted, only when other causes ruled out.
DIY?
Can I fix it myself?
You can do four safe checks:
- Confirm the controller is in HEAT mode (not FAN-only)
- Set the thermostat well above current room temp
- Replace the return-air filter or thermostat batteries if applicable
- Cycle the unit's isolator switch off for 30 seconds, then back on
About 25% of "blowing cold air" calls are sorted by check #1 alone. If those don't fix it, anything inside the heater needs a licensed gas fitter under SA's Plumbing, Gas and Electrical Services Act 1995.
When to call
Call us today if
- The four DIY checks didn't fix it
- You can hear the igniter clicking but no flame
- The heater fires briefly then drops out (then fan keeps running)
- You see an error code on the controller (have the brand and code ready)
- The system hasn't been serviced in 2+ years
Honest pricing
How much will the repair cost?
2026 Adelaide pricing, GST included, no call-out fee. Diagnostic included in the repair price.
- Filter replacement: $80 (or free with a service)
- Thermostat replacement: $260–$420
- Flame sensor clean: $45–$140
- Igniter replacement: $260–$330
- Gas valve replacement: $400–$650
- Limit switch + service: $260–$340
- Control board: $480–$950
If the unit is over 12 years old and the repair is more than 40% of replacement cost, we'll honestly say so. No upselling.
Response time
How quickly can you come out?
Same day across Adelaide metro if you ring before 10am. Most "blowing cold air" diagnostics are 60–90 minutes on site, and most are resolved in the same visit with parts off the van. After-hours rate $249 if it's making the house unliveable in the cold.
FAQ
Heater blowing cold air — common questions
The fan runs but the burner isn't firing — or it fired briefly and dropped out, leaving the fan on cool-down. Common causes: controller in fan mode, gas valve stuck, ignition failure, dirty flame sensor, or controller/board fault.
Check first — many controllers have a FAN-only mode that runs the fan without firing the burner. If it shows FAN, switch to HEAT and set 5°C above room temp. If already in HEAT and still cold, you've got a fault.
Diagnostic plus minor repair starts around $260. Igniter $110–$180, flame sensor clean $45–$140, thermostat $180–$320, gas valve $400–$650.
You can check the controller mode, thermostat setpoint, replace the filter, and reset the unit. Anything inside the heater needs a licensed gas fitter under SA gas regulations.
Same-day Adelaide metro if you ring before 10am. Most cold-air diagnostics are 60–90 minutes on site, often resolved with parts on the van.
Related help
Other gas heater problems we help with
Heater keeps shutting off
If it fires briefly then cuts out — different fault, read this.
Error code on controller
Got a code on the display? Decode it before you ring.
Heater blowing cold? Let's get the heat back today.
Same-day Adelaide metro. Most fixes under $300. Common parts in the van. Upfront pricing.