Help with Nest install replacing Honeywell DT90E Thermostat

[wildtangent]

Hi there,

I just received a new UK Nest thermostat and am having some problems identifying how to install it. I hope someone here can help me as it seems like it should be trivial but I'm not sure how to identify the right wires!

My system is currently running a Worcester Bosch 24i Junior which has a DT10 mechanical timer on it. This I can just set to always on, so can pretty much ignore it.

There's also a Honeywell DT90E Digital Thermostat on the wall a few rooms away from the boiler unit. This has just 2 wires coming to it - connected to A (live) and B (neutral) terminals. The odd thing is that the diagram on the unit shows them to be live and neutral connections, and are the opposite way round to those I can find in the online manuals. The colours on the wires appear to be brown (live) and blue (neutral), which would match up with the diagram printed on the Honeywell chassis

Following the Nest instructions, I should be able to connect the Nest Heat Link via the (2) and (3) connections to the two supplied wires. However, the diagrams all show a Live -> Live circuit with a 3A fuse connected to this loop, which doesn't seem like what I've got.

Am I over thinking this and is it right that I just connect up what was A -> (2) and B -> (3) on the Nest Heat Link?

Clearly I am also missing power from this equation, since the Honeywell is battery powered, there is no mains going to the panel on the wall. Is it OK to wire up to a regular socket or wall outlet, with a 3A plug? Or am I supposed to wire 2 and 3 to L and N like in the "Switched Live" diagram on the Nest manual

I've attached some images of the various parts of the manuals I've been reading to get to this point. Feels like I'm nearly there but would like some reassurance! The installation most resembles configuration (A) in the Honeywell guide

The post here //www.diynot.com/forums/plumbing/nest-install-2-wire-replacing-existing-stat.398926/ has all the Nest UK Manual scanned in, so I won't re-post that.

Thanks for your help from a first time poster!

Honeywell DT90e Wiring Diagram from Manual

• wildtangent
• 28 Apr 2014
• 1

This is how the thermostat is shown to be wired up in the manual. On the diagram inside the...

Worcester Bosch 24i Thermostat wiring diagram

• wildtangent
• 28 Apr 2014
• 1

This is probably one of the 2 ways the Honeywell is wired up to the boiler. I'm guesing the top...

 

[Dean744PiN5]

The nest thermostat is low voltage and should never be wired to the 240v main, this is what the heat link is for so the 2 wires at the thermostat go into t1 and t2 at the heat link and no where else.
For the mains side and switched live to the boiler, unfortunately to get to the electrics of your boiler the case has to be removed which has a integral combustion seal that is there for your safety and requires a gas safe engineer to remove and refit.

 

[wildtangent]

Hi thanks for replying

I'm talking about the Heat link, sorry should have been more clear in the original post.

The diagram seems to show that (2) and (3) are the ones handling the switched live on the Heat Link - this seems the same circuit as the A and B circuit on the honeywell unit.

Any further advise appreciated. Will post a photo of the inners of the current connections

 

[Dan Robinson]

Seriously, call a professional.

You need an RGI to work on these boilers and if you can't follow Dean's electrical advise, you are in danger of causing yourself a very expensive repair.

 

[wildtangent]

Thanks Dan

I don't intend to go poking around in the boiler itself, thats for sure. Dean's advise was regarding plugging mains into the Nest control unit (the round bit) which I was never planning to do (my mistake in the original post).

Here's my Honeywell with the fascia removed

Untitled

• wildtangent
• 29 Apr 2014
• 1

I hope that will establish how this thing is wired up and at least so I know what to say to a professional tomorrow to save some time

Thanks again!

 

[Dean744PiN5]

http://certified.nest.com/certified_finder2#/ if you find someone local to you they can have it installed in no time and safely

 

[Dan Robinson]

You don't need to tell a professional anything tomorrow. He'll work it out in about 30 seconds.


How that backplate is wired up is largely irrelevant as the two wires can only do one thing with Nest.

 

[wildtangent]

Thanks Dan and Dean

Just seems like a lot of cash for 2 wires to get connected. If it's more than that, then yes, a professional install will be the only answer since I'm not certified to do anything else with the electrics or gas systems.

If it can be worked out in 30 seconds by them, isn't it also clear from the information I've provided? Very grateful for your help of course, I just want to be sure I can't do this myself.

So my nearest are
http://www.boileraid.co.uk/ @ £60 install which seems a bit cheap considering most claim a £99 install.

I've heard a few bad stories via this forum, any advise for a london based install firm

 

[Dan Robinson]

Well it isn't just connecting 2 wires... it is knowing how to connect it after looking at the system for 30 seconds.

It travelling there.

its being insured to work in other peoples properties.

it is being qualified to work on multiple appliances.

It is being registered to work on the appliances.

It is paying for back office work to allow the field work.

It is paying for the continual training and improvement that decent companies undertake.

It is paying wages

It is paying for tools.

It is paying for literature, websites, mobile phones, uniforms, vehicles, consumables, lunch, test products, accountants, free surveys and all the other things that the customer doesn't actually see when someone turns up and does something in 10 minutes that might have taken them a whole afternoon.

£60 in London is far too cheap IMHO and you could end up having "extras" loaded on top.

As for reliable Nest installers in London - Dean and I couldn't possibly comment .

 

[Dean744PiN5]

As has been said though to wire your heat link you need to open the combustion seal on your boiler which requires a gas safe engineer and it is against forum rules to give advice that could lead to diy work on a gas appliance.
For safety, peace of mind and a professional installation £60-£90 is not bad, plus if they fook it up it wont come out of your pocket

 

[wildtangent]

OK, I realise, a professional has many overheads and expenses that come as part of the job. That's not really what I'm saying though. The rate is fair enough for the job it is. I also work in a technical industry that no-one on the outside really understands how it works (internet tech). I just don't really want to pay if it is a job I can do myself with a small amount of guidance. I like to learn how things work not just have it all done for me.

I came on this forum to try to understand whether I could simply move the two connections from one very simple control device to another. If that's not what needs to be done, then, yes, I'll happily defer control to the professionals.

Perhaps I can get some other things done at the same time, my radiator makes an infuriating ticking noise as well (comments?).

I can't quite infer from your final comment, whether Dean or Dan do or don't cover London areas.

Dean thanks for the advice, from that I suppose you mean for the 240v power, which definitely seems to be the main sticking point here. Problem is my thermostat control is 3 rooms away from my boiler so running new power to that point will probably be kinda tricky.

Can they just pull the power off from next to the boiler and install the heat link there? It will need to connect to the Nest unit in the next room - how powerful is the wifi link there because the wifi in the bathroom is a bit low signal already. Does the heat link connect directly to the Nest or is is via the main wifi router?

Thanks again guys!

 

[Dean744PiN5]

To wire the heat link to your system you will have to get into the boiler there is no other way, which is why we cant give advice.
However just to confirm are you putting the nest thermostat in the same place as your old stat and where was you thinking of putting the heat link?

Romford is about as far as i like to go into london

 

[Dan Robinson]

The Wifi signal should be OK - we're not talking HD media streaming... maybe a few hundred bytes per minute. So I would have thought a stable enough connection would be established wherever the Nest unit ended up.


I understand how you feel about people under valuing the job.... when I was growing up (sic) everyone in the family said I should go into "computers". I even had to show the school IT teacher how to set up Windows for workgroups 3.11.


In the end I had to do the entire IT suite myself - using a single set of 3.5" discs .

Managed it in one lunchbreak too. Or was it 2?


Anyway.... I knew enough by the time I left university in 1999 to understand that I didn't know enough to earn the kind of living i wanted... so here I am.


Back to the wiring.... the user part of nest needs 12VDC.... the boiler from the boiler is 240Vac... the Heat link is powered from the main and can give power to Nest, and can switch volt free. But requires mains power to function.

London is a big city - but people do travel.... however, direct advertising on this site is not allowed.

 

[wildtangent]

Was gonna put the heat link where the honeywell was (which is in the entrance hallway), and the Nest circular bit in the living room, on the wall as described in the docs

Figured that would cause minimal disruption and there would be all the things it would need there, given it is kind of the same thing (dumb on/off switch) with a clever wifi remote control

 

[Dean744PiN5]

right that makes more sense as to what you are trying to achieve but it wont work. the wires at your hwell stat are a switch live in and live out .not live and neutral to have the heat link where you suggest you would need 3 cores a permanent live a neutral and a switch live.