Selecting a 6V Relay for Switching a 1500W Heater—Current and Voltage Ratings?

Could somebody help me selecting a 6Vrelay to drive 1500watt load. I mean the ratings for the relay that must be used??
Actually I have designed a thermostat circuit to which I have connected a 1500watt heater. As i switched on the thermostat, and as it switched off the heater first, the heater coil started fluctuating and burned out. The relay I used was simple electronic relay used in low power circuits

What is the voltage powering the 1500 watt load. And is it DC or AC?

If the heater burned out soon after switching on, that would suggest the supply voltage is too high for the heater element.

Please would you also give us this information:

Circuit diagram
Supply voltage
Heater element voltage rating
Relay contacts voltage and current rating
Thermostat voltage and current rating
Details of the function and purpose of the equipment

Then we can probably diagnose the problem immediately and even suggest further improvements !

I blv a contractor will be better but you need to activate the contactors terminal with a relay of your choice.