MH light shut off after about 2 to 3 hours of use

[doctormario777]

So I came home from work today and saw that my metal halide fixture was off. I thought "That's odd... the power switch is still on and it's getting juice" so I just turned the power switch off and waited about 15 minutes. When I came back, I flipped the switch on and bing! It worked fine! Ok cool... I'll just wait and see if it does it again. Sure enough, about two hours later the lights kicked off. This time I unplugged them and left them off. I know my bulbs are old, but it seems odd that BOTH bulbs in the fixture go out like this. Think it could be the ballast?

[Big_Pun]

is it a fixture ?? some have thermal cut offs incase it over heats....

[doctormario777]

It's a 48 inch current fixture. Any ideas how I can keep it from overheating? I'd rather not drill holes in my roof.

[lildingy]

does it have any fans built into it that may have stopped or are not running?

[doctormario777]

They all sound like they're running... I'm gonna do a water change today, I'll have a look then.

[Big_Pun]

internal or external
ballast?? if external and 250w the ballast have fans also and a thermal
switch, if that fan is out it may over heat ballast same goes for internal they will shut off if too hot. is it in a canopy ?

[OrionN]

I got some "cheap Chinese MH bulb" and my current MH did the same thing. I end up have to change the bulb and it works fine. The strange thing was that I use the bad Chinese bulbs for a few months before this happen. If you have change bulbs in the last few months, change it back and see if this happen. When I change bulbs for my MH, I always keeps a few old bulbs around so I can use this in emergency like these, or for diagnostic purposes.
For MH bulbs, the hotter it gets, the less resistant it become and sometime can overload the circuitry of the light.