Shower faucet problem

First time poster. Here's my problem.

I have an old shower system (different hot and cold water faucets). Today, when I turned on the shower, the HOT water faucet broke off and water started gushing out. I quickly turned off the water supply.

I then replaced the cartridge since all the o-rings and springs drained down when the water gushed. I put everything back together and when I turn on the water supply, the water does not stop coming out from the spout (let me clarify - it is not LEAKING a small amount, but water is coming out like the faucet is on - HOWEVER, the faucet is in the off position. When I take it to on position, the water level increases even more, but in the off position a lot of water is still coming out like the faucet is in the on position).

What is wrong?

It sounds like you did not get an exact match or you didn't put it together properly.

The cartridge is an exact match, I made sure of that. In fact, I had got a plumber just a month before to change the cartridge. I got the same one from Home Depot this time also. How can I make sure it is put together properly? Will posting pictures here help ?

I was able to fix this, I had the right cartridge but didn't put the seat and spring in the right order (had it backwards). All fixed now.

However, I am still not sure why the water burst out. What could have caused that?

The retainer cap was not tightened, or it was cross threaded, OR, the thread on the valve body is damaged so the cap does not tighten properly, and if so it may come off again.