Look in the files section at the Kywoo site ERR3 is 

Tycoon ERROR CODES

To save your time to solve the problem quickly, below are the types of errors you can identify if some issues happen on your 3d printer.

Err1: The temperature of the hotbed exceeds the maximum temperature limit; please check whether the thermal interface short-circuited;

Err2: The temperature of the nozzle exceeds the maximum temperature limit; please check whether the thermal interface short-circuited;

Err3: The temperature of the hotbed exceeds the minimum temperature limit; please check whether the thermal interface is disconnected;

Err4: The temperature of the nozzle exceeds the minimum temperature limit; please check whether the thermal interface is disconnected;

Err5: The nozzle fails to heat up. If the temperature of the nozzle does not reach the set temperature within the set time, an error will be reported; please check the configuration file settings or check whether the power supply is sufficient;

Err6: The hotbed fails to heat up. If the temperature of the hotbed does not reach the set temperature within the set time, an error will be reported; please check the configuration file settings or check whether the power supply is sufficient;

Err7: Thermal runaway; when the temperature reaches the target temperature and the device continues to heat up, please check whether the thermistor is normal.

Hi 

I'm getting err3 come up on the screen and my bed is not heating. Did you manage to solve your problem ?

Keith 

Problem fixed, broken thermistor wire under heat bed. Thanks to tech support quick response 

This is the first time I visit here and I found so much interesting information in your post, thank you.