Maybe I should explain my heating system a bit better....

It's an old back boiler, with 4 wires coming out of it. Two switch on the pump for the heating, and two switch on the boilers gas fire.

If I want heating I need to switch both on, so the water is heated and is pumped around. If I just want hot water I don't switch the pump on.

It's very old system, the back boiler is new, but the control is a bit old.

All I need to do it switch power on/off to control the system.

As far as bits go, I don't have any money at the moment, so what I do have is:-

Loads of MAX233 chips.
Loads of AT89C52/51 chips.
Lots of stripboard.
Lots of resistors and caps.

I need to buy some communications wire, and a replay or two (unless I can get some from some old equipment).

So I going to have to use RS232.

Communications is going to be for re-programming the chip only (i.e. when to switch on and off)

I might add a temperature sensor, I have some Dallas ones lying around they are SMD's but I have a deft hand and a good solering iron :-)

Chris Brooks.