you have use zener in reverse baise but in your case here it will work as a simple diode you must connect that in parallel combination with your ckt. here the zener is getting heated you might be because of increase in the reverse bais, same as if you connect a normal diode in reverse baise and you increase the reverse biase vlotage across it after a time it will start getting heated up and it might also damage the component.
here in above ckt D1 is the zener diode. you can conncet any ckt accroding your project i just pasted a simple logic here ( in the red box. but if you wont connect any ckt in red box then again the zener diode will get heated up as in you case.
nice efforts, let me know till where you have reached…