We have a boiler in our kitchen which, I guess was original with the house in 1982. It works well and has never missed a beat until this week when it has started making whistling noises. It sounds almost like the noise you get if you tried to send morse code by blowing over the top of a half empty bottle!

I really really dont want to end up buying a new one, so what's the likely cause of this and is is curable?