We recently installed WH, when we are not using hot water it has blown the top connection out 2 times. Any ideas?

Cold side? Hot side? What type of connection are you using. If it is a 3/4 compression, you need to use a lot of wrench to seat a brass ring into copper. Tell us more. Thanks.

It is where the hot water is coming out -- It is hooked up backwards so it is labeled cold. Our landlord is a skinflint and does everything halfway. It is not a compression fitting, it is a screw in adapter.

Can you post a picture of the part that has blown apart?

It is hooked up backwards so it is labeled cold.
Say what? Who installed this? Even if you fixed the leak It's not gonna work!! The cold and hot connections are labeled for a reason. As you can see by the image I put up the cold water is directed to the bottom where it's heater and raises to the top. The way it's hooked up you're going to get luke warm water Before we go any farther get some one in that knows what he's doing and reinstall the water heater corectly. I can't think of any reason for any body to deliberately install a water heater backwards. This is a first for me. Y advice! Reinstall it correctly and come back, Good luck, Tom

Even if it stayed together it wouldn't work well. As is, you are dumping cold water on top and trying to take Hot from the bottom. This equals cold showers and no hot water.

Hey guys, it is possible the installer switched the dip tube over to the hot side, Ive seen it on quit a few do it yourself installs. It will work just fine, but I agree the correct way is to pipe it correctly and leave the dip tube in the cold side.

I'm trying to find any advantage to swapping the dip tube. The heater would stall face the same way. I might believe it was a old timey that simply wanted to save some time piping except no plumber would install a compression fitting so loose it blows apart. Nah! My guess would be some goof that really did hook the heater up backwards.
Cheers, Tom

Please, explain what has blown 2 times ? Can you post a photo of that connection ? Is that PVC connection ? Thanks. Milo

It is not a compression fitting, it is a screw in adapter.[

I'm having a little trouble buying that. Threaded fittings don't just "blow off". Got to be a slip,(compression)fitting to do that.
Now we really need a picture of the fitting.
Do you need instructions on how to install a water heater? Back to you, Tom