GRaViToN

There are only two cheats for HL2, and two for Portal(that I know of). They're both in the cheats section of 'SuperCheats.com'. I have only used the cheats it shows for HL2, and they both work fine for me.
Here they are:
"
Restore Health by 25 Points:
Press : Up, Up, Down, Down, Left, Right, Left, Right, O, X

Restore Ammo for Current Weapon:
Press Triangle, O, X, Square, R1, Triangle, Square, X, O, R1. "
There are only 3 things I can think of that are going wrong. Either you are doing the code too slowly. Or perhaps you're simply doing it wrong(eg. Missing a button). And lastly, I personally have only tried this code while playing HL2, NOT 'HL2:E1', NOR 'HL2:E2'. And since on supercheats it says those cheats are for HL2, and doesn't say if they work for HL2:E1, or HL2:E2, it may simply mean that this is not a valid code for the other two installments of the series. If you are trying the use the code for HL2:E1, or E2, then it may not be working for reasons of just that. I'm not sure, I haven't checked if they work for E1 or E2. I'm going to beat HL2 before I start the next episode. But they do work for HL2. Just make sure you're doing it during game play, fast, and correctly. Good Luck!