E16
ACV
External Safety Circuit Open (e.g., Safety Thermostat, Limit Switch, Cascade Control)
Boiler shows E16, burner does not start, may be linked to external safety devices
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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.
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Possible Causes
Open safety thermostat on cylinder, Open external safety loop, Faulty wiring to external controls, Faulty safety thermostat
How to Fix / Troubleshooting
Safety first: Do not bridge or bypass safety devices. Identify why the safety circuit is open.
- Check external controls: If the ACV boiler is connected to an external cylinder thermostat, safety thermostat, or cascade controller, ensure these devices are not tripped and are calling for heat.
- Reset external stats: Some cylinder safety thermostats have a manual reset button under a cover. Only reset once the cylinder has cooled to a safe temperature.
- Inspect wiring (visual): Look for loose or broken wires in the low-voltage safety loop terminals on the boiler.
- Professional diagnosis: A technician should trace the safety circuit, test each device, and repair wiring as needed.
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Repair Difficulty
Medium
3/5
Required Part
External Safety Thermostat
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