1st super high water level, 

2nd high water level,

3rd low water level,

4t extra low water level,

(the above 4 is normal water level control inside water level sensor device)

5th Yuanda have the 5th extreme low water level detector which is inserted inside boiler tank, if in any case the normal 4 sensor get problem, the 5th one will protect what's more we have 2 flue gas temperature sensor, 6th flue gas temperature sensor in the boiler and 7th flue gas temperature sensor in the chimney

with this 7 steps protection, your boiler is 100% in safe

3 steps in steam pressure protection control: 

If you have any inquiry, feel free to contact shirley@yuanda-boiler.com