People put tv's over fireplaces all the time, but it's best to check the warranty so you'll know if you are voiding it by placing a tv in this position. I would not recommend a tv over a wood burning fireplace because there's too much heat. Electric would be ideal.

If it's a gas fireplace, and the TV remains above the fireplace while viewing, it won't be a problem having a fire going. If you used a TV mount that brings your TV down and forward in front of the fire, and it is a wood fire, use the "human" test, i.e., if it is too hot to stand in front of the fire at the same distance where your TV will be parked, the fire is too hot. The maximum temperature allowable for TVs is typically a little more than 100-degrees Fahrenheit. You may consider building a smaller fire with less wood. Also, in many cities in the USA new homes can only be built with gas fireplaces rather than wood burning ones. Your fire may not be hot enough for this to be a problem. If you still want your gas fire while you are watching your TV parked in front of the fire, , turn the it down a bit

Thank you both for your responses. It has solved my problem completely!

Great!