Drayton Mid Position valve wiring

[Davej100]

I have just replaced the mid position valve in my gravity fed central heating system as it was partially seized. When I came to fit the valve control box which came with the new valve I noticed that the wiring for the old control box had the white wire not connected to anything. The wiring diagram which I had showed that this should go to the thermostat.

The system had been working fine up until now with the hot water and central heating coming on and going off when they should so I put the control box from the old valve unit on the new one. They looked identical anyhow.

The system works fine now but I am at a loss as to why the white wire is not being used.

The thermostat is a British Gas RS2 which I understand, from some info I found, can have two or three wires connected to it. The initial wiring installation was done by a qualified electrician but he did take over six hours to get it all to work.

So to summarise, I don't really have a problem as everything is working fine but would like to understand how it works.

 

[AGAS]

look at the honeywell website will show you what you want know ( very good site ) . plus is not advisable to get electricians to do heating systems generally , get heating engineer.

 

[DP]

Six hours tad long but he possibly struggled o wire up but gold star nevertheless for completing the marathon

When you select hot water at the programmer, boiler is fired by the cylinder thermostat Nd valve stays unoperated. Oncce water heated to set temperature, boiler switches off

If during heating of hot water, CH activates and heating demand required, valve moves to mid position. Assume HW now up to temperature but CH still active- valve moves to shut HW port

CH now up to temperature, valve either stays in this position or restores to home position and boiler demand removed

 

[Davej100]

Thanks for the explanation DP. My system seems to be working as you describe even without the white wire connected. The only thing it may be doing without me realising is that when it's heating the hot water and the CH kicks in it may not achieve the middle position. It may switch fully to CH and then return to hot water when CH is satisfied. I would not have noticed this.

Surely something must be misbehaving with no feed to the white wire.

Added 14:37 - I have just checked and it is indeed doing this. It never goes to the middle position. CH takes precedence and if hot water is calling for heat it only gets it when CH does not need it. Electrician who fitted it obviously did not know how it was supposed to work and has bodged it. I'll get this sorted.

 

[Phill Peck]

Is the wire just hanging there or does it have a choc block on the end of it

 

[dilalio]

This will explain it all...
http://octaveblue.co.uk/c_heating/hw1_ch1.htm

And this describes all the other possible states...
http://octaveblue.co.uk/c_heating/

 

[Echo the husky]

Which valve head do you have? How can a mid position valve move without power to the white wire? The grey wire is internally disconnected via the first switch until the valve is at mid position. If the valve is at mid position due to power on the white wire, switch one operates connecting the grey wire. When power is then applied to the grey wire for hot water off (but heating on) the valve can then go all the way over to heating only.

Without the white wire connected it can only be at the hot water only position, which the mechanism spring returns to. The other option is this isn't a mid position actuator.

Internal mid position valve wiring.