Cylinder stat

[currie123]

Hi guys

What is the purpose of the third connection at a cylinder stat which appears to connect to the central heating pump on most wiring diagrams I have seen?

The system I have is what I assume to be gravity hot water with pumped central heating .

There are no motorised valves, just a pump switched on from the CH on terminal at the programmer, and the boiler switched on from the HW on terminal at programmer. I am to install a cylinder stat and I understand that it is just a switch to cut power to the boiler once temp rises, but not quite sure what purpose the number 2 connection has that appears to connect to the pump live?

When heating is selected at the programmer both the hot water and heating come on. Heating can be selected independently.

Thanks

 

[davesparks]

C is the common, 1 is the N/O and 2 is the N/C. So C and 1 gives you a break on rise or 'ON' and C and 2 gives you a make on rise or 'OFF'

You can't just chop a cylinder stat in to a standard gravity system, the hot water channel fires the boiler and the heat gravitates to the cylinder with no temp control and then the heating channel and roomstat just operates the CH pump.
If you chop a cylinder stat in to the system then your heating will cut off once your hot water is up to temperature.

The common way to get a degree of temperature control over the hot water is to install a 2 port valve on the flow pipe to the cylinder and control this with a cylinder stat fed independently from the boiler system (usually fused from the I/H circuit as its the nearest supply).

 

[currie123]

Ok thanks.

So the cylinder stat would be positioned on the cylinder or on one of the pipes?

And could you explain how the cylinder stat and 2 port valve would be electrically connected?

 

[davesparks]

Ok thanks.
So the cylinder stat would be positioned on the cylinder or on one of the pipes?

Seriously? the clue is in the name!

And could you explain how the cylinder stat and 2 port valve would be electrically connected?

Simply connect the cylinder stat so that the valve motor is energised when the temperature is below the set-point of the stat, you won't need the microswitch in this arrangement.

I'm surprised and electrician can't work that bit out for themselves

 

[currie123]

Thanks for explaining Dave yes a bit embarrassing at least I will know next time.