Luke

[Nightmare1308]

MDJ andMarvo much appreciated for ur help and thanks to u no i finally understand it !!! Lol ill put it into practice Monday when I have another look at it thanks alot to you

 

[SYKRAPS]

If there is a no demand from the controls then the NO contact is open and the NC contact is closed basically in their normal un-energized state between them and the common conection, but once there is a demand from the controls (ie it is turned on) they are no longer in their normal un-energized state and NO closes and NC opens to the common connection. Volt free is the state of the terminals in normal operation, many time switches can be used and adapted for both volt present and free installs but always read the control and boiler instructions carefully to confirm as some appliances can be damaged by the presence of mains voltage beyond repair. If in doubt contact the boiler manufacturer as they are usually helpful and will confirm whether the control side requires mains voltage to opperate or not, also from my experience the vast majority of domestic boilers require a 3a fuse to protect the pcb board and internal controls.