Do I need a new water heater?

[silark]

I found we did not have any hot water the other night so suspecting the pilot had blown out I went down and it had so I lit it and turned it on. I heard the main burner light. The next day we still had no hot water so I checked again and the pilot light was out. This time I watched what happened when I turned the heater on:

1. pilot stays on after releasing the pilot button

2. turn the heater on and the pilot light goes out and the main burner does not ignite

After several attempts the same thing happens time and time again and I notice as I am switching the heater on the pilot light lowers the closer I get to the on position. I did manage to get it lit by slowly turning the valve to on and just at the point the pilot light was about to go out the main burner lit but seemed to splutter for want of a better word. It just wasn't a constant flame it seemed to pulse. Anyway after coming home about two hours later the main burner is out and the pilot is still lit. From my research the thermocouple is ok if the pilot light stays lit so is this a case of a new heater or a good clean because something is obstructing the gas?

My concern which is why I turned the pilot out is that whlist the pilot stays lit heating the thermo couple does that mean gas is still being released but not burnt?

[silark]

Ok so I just had a thought that the main burner should be off as the water had reached it's desired temp. Is this correct? If so what you make of the other stuff?