Is it safe to use my 240 volts heater through a 250 volts extension cord?

I have a heater thermostat that can run at a 240v power outlet. Since its cord is too short and the power outlet is high up on the wall close to the ceiling I decided to use an extension cord. I have a 5m cord that is 250v, 10 A. Is it safe to use the heater through this extension cord?
Asked Jun 14, 2016

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