Cooling system problem!
 

Need some help, on sat morning my discovery 1 300 tdi overheated! got it to cool down without takin the cap off cause i had no water to replace it. pulled out on the road and it heated straight up again, pulled over, got some water, cracked the cap and there was plenty of water in there, got home, couple hours later checked the water, nothing in there, filled it up, has nt got hot since but i have nt taken it far, Sun afternoon, the water was pissing out of the water pump, so just put another water pump on but im not convinced i ve solved the problem, it bubbles up a bit if there s to much water in there but i would nt call it a 4 cylinder water pump yet, (as in, not head gasget) or at least i dont want it to be, oil not got water in it, So whats going on with it, anyone help or am i worrying too much? Cheers