Boiler and Pump Circuit

[Ohm From Ohm]

We are working on a very old heating system where the boiler and pump can be activated independently by the CoH control and the H.W. control. The problem is if C.H. is activated we don’t want it to back track onto the H.W. circuit, and vice versa. The only time this is acceptable is if the C.H. is on – then it’s OK to select H.W. We have experimented with 8 + 11 pin relays without success.

The only cables available are the switch wires from C.H. + H.W. + N + E, and outgoing L + N + E to the boiler and pump.

 

[Knobhead]

Sounds like an old Landis & Gyr C/heating switch. Look on the back, there's a 2 position cam to select the options. No need for any relays.

 

[mountainman]

If it is an elderly system with gravity HW and pumped CH then you cannot have CH on without HW as the boiler won't fire.