Help wiring Nest Heatlink

[Ian Roberts]

Hi, seen some good help with installing Nests on here so hoping someone can help me too. I'm trying to replace a honeywell Smartfit thermostat with a Nest to control my Glowworm Ultracom Hxi boiler.

I've thought to wire up the heatlink in to the existing wiring centre for the smartfit then detach the thermostat leads and repurpose them for the T1 and T2 connections to put the Nest in place of the existing thermostat. Happy with that bit, got L, H and E across to the heatlink easy enough too and trying to follow the Y plan wiring instructions to get this set up but just not entirely confident with how what I'm seeing matches up with the instructions.

I've attached pictures of the wiring centre I'm hooking up to and the Y plan wiring diagram from the Nest instructions. So far, I have L and N from the mains supply across to the Heat Link. I've jumpered live across to 2 and 5. The wiring diagram seems to refer to colour coded cabling that doesn't match what I have though and, not being an electrician, liberal use of the word "common" is throwing me a bit too so I'd really appreciate some advice on what I need to put to 3, 4 and 6 in the nest. I'm thinking one from the Boiler grouping (White to 3?) and one from the Pump group to 6, then it appears something common to both to 4. I'm just not sure so would really appreciate any help anyone can offer. Even if that is "Stop you idiot, you don't know what you're doing". My assumptions are based on what wiring I can actually see to work with, but I'm also wondering that perhaps it should be the 3 port valve, rather than the pump, that I should be hooking up to the heatlink, which it comes in via the RJ11 port at the bottom of the wiring centre.

Any help would be greatly appreciated and if there is any more information I need to provide, then please just let me know.

Many thanks

 

[picasso]

Sorry to be the bearer of bad news but the nest is not compatable with honeywell smartfit systems.

 

[Ian Roberts]

Apology accepted! Thanks.

I was rather coming to that conclusion myself, though it wasn't (last time I looked at least) on their list of incompatible systems so I was hoping there might be a chance.

Accepting that that is the case, is there a reason for that do you know, and is there a work around? i.e., is there an alternative smart stat that would be compatible, or is there a way to take the smartfit itself out of the equation? I was trying to work with it to maintain things like the cylinder thermostat for instance in the existing wiring centre but take it the smartfit is a little more sophisticated then than just a wiring centre. No way for the 2 to co-exist for instance if I only wanted the Nest (or A.N Other) to control the heating rather than the hot water?

How complicated would it be for instance, to replace the actuator on the 3 port valve with something less proprietary to the smartfit?

Happy to be told that this is a dead end, just like to understand why it's a dead end.

Thanks for your help

 

[picasso]

There is a workaround if your reasonable with electronics, there is a thermistor in the Honeywell room stat/programmer that you can fool using a couple of resistors and a relay controlled by the nest, there is a blog somewhere on the nest site but I cant find it at the moment.

 

[Ian Roberts]

That sounds interesting, thanks, I'll have a look for that myself too.

 

[Ian Roberts]

Hello again. Other projects meant this took a back seat but I'm hoping to revisit it. Unfortunately, couldn't find anything on the thermistor hack mentioned by picasso.

Would really appreciate if anyone has any pointers on that, or any other practical suggestions as to how to best go about this.

Failing that, thinking to possibly ditch the smartfit altogether and replace with more bog standard wiring centre, 3 port valve and cylinder stat.

Thanks in advance for any advice or information anyone can give me.

Cheers

 

[picasso]