Wiring In A New Room Stat

[raybush]

I'll describe the type of central heating system i have.
Ideal boiler with a pump next to it a room stat in the hall and a clock to control the on and off times of the system.The system also has gravity hot water heating via the boiler.
The room stat that i currently has fitted is over 20 years old and an old brown coloured Honeywell type ,the stat has only TWO wires running into it which come from a small junction box that has wires from the timer ,pump etc.
All i want to do is to safely remove the old stat from the wall (easy job) and fit a new one .
I'm assuming that both wires (when the room temp gets too low) send current to the pump and away it goes.I assume that one wire must be live ,but am not sure what the other one does .
I hope this doe'snt sound messy and was hoping for a bit of guidance with my two wires onto my new stat.
Thanks

[raybush]

Thanks for the answer.
What i'm trying to find out is what the two wires do.
I know that the stat switches the pump on and off,but just need to know how the two wires controll things.

[BRIGHT SPARK]

What stat are you fitting?

[raybush]

Hopefully i'll try and obtain a mechanical type (possibly a Honeywell) the same as i've got now ,but a newer version.........something that runs with the two wires that i've got now.

[BRIGHT SPARK]

Ray......in that case try live (or red or brown) to term1.....and the second wire to term 3. As you dont have a neutral or earth ask for a stat that does'nt require them. The stat works just like a temperature controlled light switch.Confirm that the circuit is dead before messing........just because the wires are small...it still hurts!

[raybush]

Thanks for the help,i'll give it a try over the next few days.