Technical

Greetings all, for my first post here. So recently I made a purchase of a relatively unused Mallard set which had never been run before. So once I received it of course I tried to run it, keyword there being "tried". While steaming up, the engine was letting off a lot of steam, at the time I didn't know if it was supposed to do that or not. Once the engine was shooting off nicely, I attempted to try and get it moving on the rolling road. This didn't happen, I went a few clicks forward, green but nothing. So I tried going backwards, red, then a whistle, then it kept whistling, and nothing. So I let it cool, tried to do some research and it seemed the problem was similar to one of the troubleshooting problems in the given manual, with the solution giving something like "adjust the valve position so that the red light shows and the whistling stops". Once the engine had cooled I took the body off and inspected, nothing seemed off from other photographs I found online, I unscrewed the top of the pressure release valve and checked it (I thought it had something vaguely to do with Hornby's vague solution), then replaced it how I found it. I tried steaming it up once again, this time to continuous whistling from the get go, however no leaking steam from what I saw, however I didn't steam it up to the point where the pressure release valves were blowing off. I should also mention that water was leaking through the overflow valve whenever the whistle was going off.

I get the feeling this is a problem that could be caused by age, however being completely new to this I have no real idea. Any help, ideas or advice would be much appreciated.

Thank you all.