Hurlcon MX Heater F4 Error – Flame Rollout Fault (Dangerous)
If your Hurlcon MX series gas heater is displaying an F4 error, this fault relates to a flame rollout safety shutdown. Flame rollout occurs when the burner flame does not stay correctly inside the combustion chamber and instead rolls forward, which is dangerous.
Note: These Hurlcon heater error codes and faults also apply to AstralPool HX and JX gas heaters, as they are the same heater models rebranded under AstralPool.
This error is detected by a flame rollout sensor designed to shut the heater down immediately if unsafe combustion is detected. If you see an F4 error, do not continue attempting to run the heater.
What does the F4 error mean on a Hurlcon MX heater?
The F4 error indicates the heater has detected flame rollout. Under correct operation, the flame should burn cleanly and vertically within the burner chamber. When airflow is restricted or combustion conditions are poor, the flame can search for oxygen and roll forward toward the front of the heater. The rollout sensor triggers and shuts the heater down to prevent fire risk and damage.
What causes flame rollout?
Flame rollout is typically caused by restricted airflow through the heat exchanger or combustion chamber, or by incorrect combustion conditions. Common causes include:
- Heat exchanger blockage from leaves, insects, debris, or built-up rubbish
- Restricted ventilation around the heater (insufficient oxygen supply)
- Blocked flue (where a flue kit is installed)
- Incorrect gas pressure causing poor combustion and sooting
- Soot build-up from lack of servicing or incorrect combustion setup
- Heater not being serviced regularly (combustion chamber contamination over time)
Why the F4 error is serious
Flame rollout is not a normal operating condition. It can indicate unsafe combustion, overheating, or fire risk. The rollout sensor is a critical safety device and should never be bypassed or ignored.
What you should do immediately
- Turn the heater off
- Isolate power to the heater at the power point
- Do not attempt repeated resets
- Book a licensed gas fitter to inspect the heater
Professional inspection is required
An F4 flame rollout fault requires professional diagnosis and servicing. A technician will typically inspect the heat exchanger and burner chamber for blockages, confirm correct ventilation, check the flue (if installed), and measure gas pressures to ensure correct combustion.
You can book a Hurlcon MX heater service with HeaterFix for professional flame rollout inspection and repairs.
For a complete list of gas heater error codes and troubleshooting guides across all brands, see our Gas Pool & Spa Heater Troubleshooting Guide.
Need help with a Hurlcon MX F4 error?
This article is provided for general information only. HeaterFix recommends all gas heater servicing, repairs, and replacements be carried out by a qualified licensed gas fitter.
