Nest with 3 port valve system

[drauk]

I am trying to install a Nest thermostat. It's replacing a wireless Honeywell thermostat and connecting to a Potterton boiler downstairs. Upstairs in the airing cupboard is a hot water tank, a pump and a 3 way valve next to the tank.

At the moment the call for heat on the Nest Heat Link is connected to the Switched Live on the boiler, as per the Nest installation guide.

As things stand right now, the Nest calls for heat in the appropriate way and it fires the boiler. However, this doesn't send the signal to the 3 way valve to actuate to provide flow to the radiators. If I pull the level across and latch it then water flows to the radiators.

The only other way to get the three port valve to switch to flowing to the radiators is by turning up the old thermostat, which causes the old programmer (set to "Constant") to tell the boiler to fire AND presumably tells the three port valve that heating is required. But of course that's no good, because then the heating is not being controlled by the Nest.

So, how do I get the Nest to switch the valve? There doesn't seem to be any wires related to the valve anywhere near the boiler (the boiler is in the cloakroom, the programmer is on the wall in the kitchen, the valve is upstairs in the airing cupboard). Having looked at how the three port valves work there are several connections and I'm not sure which one would use, even if I had access to the wires which I don't seem to.

Would one connect the Nest's call for heat to one of the wires to the valve and if so which?

And any clues as to where those valve wires would usually end up downstairs - at the programmer or at the boiler (neither of which are apparent)?

Or have I got something else completely wrong? If photos or diagrams would help please let me now and I'd be happy to post them.

Thanks in advance.

 

[igneous]

Heating and hot water wiring isn't rocket science but how it has been carried out can some times confusing, I've not personally dealt with nest, you may get better advice in the electrical forum. Your system is probably priority hot water. As I say I'm not familiar with nest but it probably prefers a s plan system

 

[Agile]

The Nest like all modern thermostats has a two wire "volt free" output which connects in series with the heating timeclock output and thats usually to replace the existing room stat.

Read the installation instructions carefully so that you can connect it correctly as they are expensive if you damage it by wrongly wiring it yourself.

Tony

 

[xr4x4]

Ermm...why is the old thermostat still connected..?

 

[drauk]

Heating and hot water wiring isn't rocket science but how it has been carried out can some times confusing, I've not personally dealt with nest, you may get better advice in the electrical forum. Your system is probably priority hot water. As I say I'm not familiar with nest but it probably prefers a s plan system

I'm not aware that Nest is specifically Y or S plan. After all, it's a call for heat mechanism. Other people seem to have it working with either.

 

[igneous]

Well then it's an easy wire up, carry on

 

[drauk]

The Nest like all modern thermostats has a two wire "volt free" output which connects in series with the heating timeclock output and thats usually to replace the existing room stat.

Read the installation instructions carefully so that you can connect it correctly as they are expensive if you damage it by wrongly wiring it yourself.

Tony

The installation instructions don't talk about wiring it in series with anything. They state you simply connect live and neutral, bridge the common connection to live, then connect the call-for-heat.

 

[drauk]

Ermm...why is the old thermostat still connected..?

Well, it (the old, original thermostate) is wireless. So there isn't anything to disconnect as such. I can (and have) dial it down to zero or take its batteries out. This stops the current controller trying to control the heat and leaves the job to the Nest. But that's the problem; the Nest doesn't control the valve in the way that the original system did.

 

[igneous]

So after you've carried out those connections, once the old thermostat is removed it's all working fine?

 

[drauk]

So after you've carried out those connections, once the old thermostat is removed it's all working fine?

No. As per my original post, the Nest calls for Heat and that fires the boiler, but it doesn't actuate the 3 way valve which directs the hot water to the radiators.

 

[igneous]

LOL

 

[drauk]

LOL

Huh?

 

[igneous]

So you've removed the reciever which the "wireless" thermostat controls?

 

[drauk]

So you've removed the reciever which the "wireless" thermostat controls?

No because that's the controller for the hot water. And indeed, presumably the controller for the 3 port valve - or is that usually controlled by the PCB within the boiler itself? For what it's worth and for completeness, if I switch the controller off completely I unsurprisingly still have the same issues as described above.

 

[picasso]

The white wire (of the 3 port)is what you need to control not the orange, basically live and neutral to the heat link, connect live and 2 together then white from 3 port to 1 on the heat link, OR get someone that knows what they are doing.