Boiler display shows A05; unit may not fire and indicates low water or flow fault.
Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
Possible Causes
How to Fix / Troubleshooting
Safety first: Turn OFF power to the boiler. Allow the system to cool before opening any valves or strainers. Relieve pressure as required by the installation manual.
Steps:
- 1. Verify valves are open: Check all service and isolation valves around the Raypak boiler. Ensure supply and return valves are fully open.
- 2. Clean the system strainer: If a Y-strainer or inline filter is installed on the boiler loop, isolate it, relieve pressure, and remove the strainer cap. Clean the screen of debris and reinstall with a new gasket if needed.
- 3. Bleed air from the system: Use automatic or manual air vents to purge trapped air from the boiler and near-boiler piping. Air pockets can prevent the flow switch from closing.
- 4. Inspect the flow switch: Locate the flow switch on the boiler piping. Check wiring connections. If accessible, gently move the paddle to ensure it is not stuck. Mineral buildup may require removal and cleaning or replacement.
- 5. Check circulator operation: Confirm the boiler or system pump is running when there is a call for heat. A non-operational pump will prevent flow and keep the flow switch open.
If A05 persists after confirming flow and cleaning strainers, the flow switch or control board may be faulty and should be tested by a technician.