Smart thermostat Q (again).

You provided a photo of the boiler end, but did you say what the make/model of boiler is?

Is it fair to assume that the neutral wire isn't connected to anything on the existing stat? There was probably a mechanical stat in the past, which needed a neutral for its accelerator heater. The neutral will have become redundant when the mechanical stat was replaced by a battery powered one.

Sounds like the new stat is mains powered, and has 'volt-free' contacts to allow it to switch low voltages rather than mains if required. To switch mains, simply insert a link between L and one side of the switch, like you say.

Yes, currently blue wire is floating (well terminated with a connector).

Ah, that's interesting. Makes sensen

Well more scouring and digging into Amazons (excellent) customer comments with pictures shows exactly that setup from a happy customer. So I feel a lot more confident.

Looks like that'll be tomorrows job.

Sorry, Vaillant TurboMax 824.

But it seems another Amazon customer had a similar setup to me, and solved it as I thought (jumping L to one of the dry contacts).

that works if it is a true smart stat and there is no external timer involved

Yes. The clock on the boiler broke about 5 minutes after we had it (I exaggerate slightly, but it didn't last 3 years). Which was one of the things that prompted me to get a replacement programmable stat.

Now "Smart" things are affordable (I think this smart stat was cheaper than the programmable one) then it seemed the best way to make the heating accessible for SWMBO.

So the boiler is set to heating on permanently, and then the stat does the timing and statting.

Your photo shows the black and grey wires on pins 3 and 4 of the boiler,

just connect these to pins 1 and 2 of the stat as per the "GC" diagram.

page 20'ish

No need to link anything.

Sadly, further treble checking shows that the wires at the stat are *not* the wires out of the boiler. Hence the re-posting.

I thought it was too good to be true. Turns out I was right ...

Needing to turn 3 wires at the stat into 4 means there is :(

where does that 4+E from the boiler go to then?

F*ck knows. I didn't fit the boiler wiring.

Bottom line is I have L+N + (i'm guessing) call for heat at the stat end. I have no intention of crawling all over the loft to mess around with wiring unless it's life or death, so have to make do.

Since I've already had a regular 'stat and programmable 'stat working here, there should be a way to get the snart 'stat working.

I'm cheered by seeing pictures from other people who have jumped L to one of the dry contacts and the other dry contact to the call for heat wire.

(If you want an idea of the skillz of the guys who fitted the boiler, then about half way through the job, they started saying they hadn't realised our bungalow was as big as it was. If I'd been paying them, they would have gotten a Jethro broadside. But it was a present from the MiL, so I said nothing).

multimeter available?

measure A/C volts between N and pin 3, and between N and pin 4 at the boiler end when the stat is calling for heat and when it is not.

you'll probably fond one of them is a permanent live to the stat, the other is a switched live returning from it ... if so you can link L to e.g. pin 1 of the stat and then feed pin 2 back to whichever of 3/4 at the boiler end is not perm live.

A hidden "wiring centre" aicmfp

You would imagine with all these smarts some smart advice on wiring these things up might be provided? Brian

That's exactly what I did with mine (Honeywell TR4 and WB Greenstar boiler).

Many thanks for all who responded. Thermostat is in, and up & running.

Notes:

2) As usual, despite me having a brand new patress box, the screws supplied with the unit didn't fit. Luckily I had some 20 year old ones that did (only experience can tell you nothing is *ever* "standard").

4) Pairing with wi-fi was a doddle as was installing and configuring the app. So no real need to actually see the display on the unit.

Oh, just remembered another "gotcha".

As supplied, if you screw the backplate to the patress box, the slight recess means you'll never get the front unit to slide over. I had to use