Replacing Horstmann C27 with Nest

[simps100]

Hi all,

We have bought a new Nest Thermostat to replace our current Horstmann C27 which runs our Central heating and Hot Water on a timed system, we have a Netaheat Profile 303 Boiler.

Having a few issues wireing in the Nest Heatlink - mainly trying to work otu what the current Common and Call-For-Heat connections are - have been looking at http://www.horstmann.co.uk/files/86..._guide_CentaurPlus_C21-C27_installer_web1.pdf but havent managed to work it out my self , we also have one thermostat on the system which will be replaced if that helps.

Any help would be much appreciated - if any more info is required please let me know.

Thanks

Marc

 

[flameport]

The Nest is a thermostat - it replaces the thermostat you have already got.

The C27 is a programmer which also controls your hot water - you will still need this to set the on/off times for your hot water.

 

[simps100]

Oops my bad i meant to say to replace the heating element of the controls and the C27 will remain in place controlling the hot water - problem im having is finding there to connect the heat link into the existing cabling.

 

[jackthom]

Try to find where the existing room thermostat is connected at the wiring centre. That's the best place to connect up the Nest Heatlink.

If you can post a picture of this wiring I'm sure someone will be able to help.

 

[simps100]

Ok done some more searching!

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• simps100
• 30 Dec 2014
• 1

This is the existing thermostat which is in the living room wired as it has been.

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• simps100
• 30 Dec 2014
• 1

This seems to be the other end where the programmer is (the white cable with the blue wire with yellow tape around it)

The Yellow cable from the Thermostat goes into a choc box which you can see in this picture connected to a white cable

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• simps100
• 30 Dec 2014
• 1

-

That white cable goes off into a honeywell valve.

The red cable coming from the thermostat goes into the existing C27 programmer in number 4 on the white box

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• simps100
• 30 Dec 2014
• 1

Hope ive made this clear- Thanks for your help

Sorry some of the images seem to have uploaded the wrong way up!

 

[jackthom]

The red cable from terminal 4 of the programmer will no longer be required and should be removed from the programmer and made safe (unless for some reason you want the programmer to still have some control over the heating which the following does not allow for).

The Nest Heatlink will need the usual Live and Neutral, from the same supply as the programmer etc, for it's power.

A short wire Link is required from the Heatlink Live terminal to terminal 2.

The yellow wire that was connected to the old room thermostat should be removed from the block and instead a wire from this connector should go to the Heatlink terminal 3. This becomes the new feed to that white wire which powers up the motorised valve when heating is ON.


Are you supplying power to the round Nest Thermostat itself using the USB style mains adapter?

 

[simps100]

Just done that and its all up and running - Thank you so much - Saved me alot of money there getting it installed.

Reused the old Thermostat cable into T-1 and T-2 to power the Nest Thermostat.

Appreciate all the help

Marc

 

[simps100]

Hi All!

Almost a year on and im here again! Thanks to your help last time we've had nest up and running all year with no issues atall, with them announcing the 3rd Gen with hot water control we've ordered that and managed to sell our current nest already which is great.

Now im after some help getting the hot water element up and running with the new nest to completely replace the Horstman C27.


So here is the wiring layout for the new nest with hot water controls


And this is what we have remaining for our horstman C27 which is controlling only the hot water now. -so the neutral and live on the left will come out will go straight into the new nest heatlink. Just wondering if somone could advise where the grey and white cable currently in number 1 and the brown one in number 3 will go within the hot water part of the heat link.

Thanks in advance!

 

[jackthom]

1 in the c27 will go into heatlink 4
3 in c27 will go into heatlink 6

Then you need a short wire link from Live to 5 in heatlink

 

[simps100]

Great thanks sounds easy enough - currently there are 2 cables in 1 (the grey and white ones) - i assume i can put these 2 into a choc block and a wire from there to number 4 i the heat link?

Thanks for your help again!

 

[jackthom]

If those two wires will reach and fit together into number 4 that's preferable. If not a choc block would be OK.