Thermostat wiring

[Mr Larrington]

O hai!

I am trying to make sense of how to replace my cranky old Honeywell thermostat with a spiffy new wireless thermostat plus receiver.  I am failing, because electricity is a particularly arcane form of witchcraft.  The wiring inside the current ha ha installation looks like this:


Inside old thermostat by Mr Larrington, who apologises for the highly non-standard colouring of the individual conductors.  Inside the cover it says:


Inside old thermostat 2 by Mr Larrington, on Flickr.  TFM for the old one says:


Old thermostat wiring diagram by Mr Larrington, who also apologises on Honeywell's behalf for the fact that the numbers in TFM do not actually correspond to the actual numbers actually moulded into the actual hardware.

The wiring diagram for the new receiver looks thus:


New receiver wiring diagram by Mr Larrington, on Flickr

My dodgy boiler is actually a combi but the present wiring, at least to this untutored oaf, appears more like the “Basic” installation.  The question is: which wire to which 'ole?  Providing a separate 230-vole supply to the earth/live/neutral terminals on the left of the new one is easily accomplished should it prove necessary.

[mcshroom]

The colours aren't non-standard, they are just old

I'd agree, to me the wiring is similar to the "basic boiler" wiring. The combi-one would be for a volt-free 2 cable thermostat.
https://flameport.com/electric/central_heating/combination_boilers_thermostat.cs4

[rafletcher]

I.d be interested in what 'stat you chose.

Feanor will be along betimes to assist methinhs.

[grams]

Does the old thermostat have an indicator light on it that works?

If so, red is live, blue is neutral and yellow is switched live going back to the boiler, so "B" in the basic boiler diagram.

You can always double check by having a squiz at the other end of the wire inside your boiler, keeping a careful eye out for any Corgi double agents lurking in your household of course.

[Diver300]

I think that you also need to join L to A as in the basic boiler diagram.

[Kim]

Would concur with the above.  Red to L, Blue to N, Yellow to B, the bare wire to Earth, and jumper L to A as per the 'Basic Boiler' diagram.

Unless the boiler is clever enough to support OpenTherm (which the diagram suggests the receiver does), in which case it probably makes sense to re-wire to use that?


(Is controlling HVAC using 240V mains this side of 1973 a quirky BRITISH phenomenon?  I'm guessing it might be...)

[Mr Larrington]

No lights on the old thermostat.

The new 'stat is a Honeywell T4R, the old one a T6360 from the late Jurassic.

The boiler – a Vaillant – dates from the late 90s; I think the wiring does too, only the 1890s.  The internets say Vaillant boilers don’t grok OpenTherm without extra kit (and doubtless ruinous expense) so that's out.  I think I'm gonna have to try to track down what happens at the other end and report back…

[Mr Larrington]

OK, at the boiler end TFM says:


Boiler TFM by Mr Larrington, on Flickr


Boiler TFM 2 by Mr Larrington, on Flickr

And in Real Life:


Boiler RL by Mr Larrington, on Flickr

[grams]

Vailiant don't seem to explicit about how 3, 4 and 5 aren't meant to be used, though looking other people's images 5 is apparently neutral and 3 and 4 are what need to be connected together to make central heating happen.

You could try connecting it as already suggested and see what happens, or you could just connect red and yellow to the A and B contacts and provide power with separate wiring.

[mcshroom]

That Agrees with the basic boiler diagram and Kim's instructions above. It looks like you have Live in 3, Switch-Live in 4, and neutral in 5.

I'd stick with taking power from the boiler. That way if you isolate the boiler you don't have it being powered backwards through the 3 connector which would be dangerous.

[grams]

That Agrees with the basic boiler diagram and Kim's instructions above. It looks like you have Live in 3, Switch-Live in 4, and neutral in 5.

I don't think we can tell which of 3 and 4 is permanent vs switched, or even (possibly being overly pedantic here) if they have exactly that intended use.

I'd stick with taking power from the boiler. That way if you isolate the boiler you don't have it being powered backwards through the 3 connector which would be dangerous.

That can't happen if you don't make a link between L and A/B on the receiver. I'm suggesting following the "combi boiler" diagram that keeps the receiver relay isolated.

[FifeingEejit]

I tried to make sense of the diagrams and failed first time...

The T6R can do both on/off and OpenTherm so it's working out how to get it to switch that boiler on/off

However...
based on what the diagram for the current thermostat shows, there's
1 240v input that's going to a switch - Red, in one state it outputs on 4 on the other it powers the 2 useful outputs
And 2 outputs,
one straight 240v to the heating load 10(3)A - Yellow
and one via the resistor neutral - Blue

Having a snoop on other discussions on T40s seems they work with a programmer, which is also replaced by the T4

https://www.diynot.com/diy/threads/honeywell-t40-wiring.359817/?utm_content=cmp-true
1 - Live from programmer CH ON terminal
2. Neutral
3. Switched live usually to motorized valve, which turns the boiler on via a microswitch. (I was simplifying things in my last post as there are several ways a boiler can be switched on.)

The cable is just old colour 3 core with separate earth, think this is fairly normal as it's a control cable not a line cable. Fairly sure the wee brother dug out 4 core 3-phase cable (he's laugh at me for that description) when he wired my T6R in.

Following the basic diagram, it'll just turn the whole thing on and off which combi's don't really do as they usually have permanent feed and switched feed. Or at least do now.


So on the boiler I make that.
3 - Red - Live to the programmer and to the thermostat
4 - Yellow - Heat On/Off line
5 - Blue - Neutral apparently

makes me think 4/5 is A/B as it's creating a switch with the difference between neutral and line.

Vaillants destructions as to what 3/4/5 are is shit though

[Mr Larrington]

The ones on the far right are most likely the OpenTherm terminals on account of being helpfully labelled “OT”.  Anyway, I decided to try the “no separate mains connection” option:


P3@r mi l33t w1r3-5tr1pp1n9 5k1llz!! by Mr Larrington, on Flickr


Totally wired… by Mr Larrington, on Flickr


Ready to light blue touch paper… by Mr Larrington, on Flickr.

No, I ent proposing to leave it like that.  Time to power up the boiler and wait for the bang…

[Feanor]

That all looks fine, assuming the boiler's terminal (3) which feeds the red wire is the Live.
That's doing double-duty now at the receiver, because of the short link wire:

1) It's providing the feed to the on/off relay (A) which will on-it/off-it the boiler via (B) and the yellow wire;
2) It's powering up the receiver gubbins via the (L) terminal.

The only query I have is: where's the timer?
I'm assuming it's built in to the boiler, then the L output on (3) to the 'stat may not be a permanent Live, it might only go live when the timer says so.
So the receiver might not get a true permanent Live.
So it won't be doing any receiver-ing during the periods when the timer is OFF.
This is not a problem so long as the receiver is happy being power-cycled in this way.

[Mr Larrington]

There’s a timer* at the boiler end with a three-position switch, viz. permanently off, permanently on and controlled by the thermostat, timer & thermostat combined.  Switch at the boiler set to “permanently on” and timer function controlled by the New! IMPROVED!! wireless thermostat wossname which I have yet to switch on…  Anyway:


Actually attached to Larrington Towers by Mr Larrington, on Flickr


Green light, heating on, no bangs or sparks 👍 by Mr Larrington, on Flickr.  Yes, it's umop-ap!sdn.  No, I don't care.


Torch for thermostat jibbling during the hours of darkness; hopefully redundant… by Mr Larrington, on Flickr

Now to do battle with the bit that uses the Devil’s Radio.

* and I remain far from convinced that it works properly due to the heating's penchant for coming on at hours 01:30 when it ent meant to.

[FifeingEejit]

These fancy new control thingymabobs take the function of timer, programmer and thermostat, so if you can removing the timer may help.

Coms between box and receiving box is probably Zigbee or some proprietary thing Honeywell have adapted to suit them.

If you press the button on the reciever and the green light goes on followed shortly thereafter by heating and press it again and the green light goes out followed shortly there after by no heating, and then can continue the cycle for ever then it's probably ok.
If the timer on the boiler cannot be removed, and it turning on or off causes the above cycle to stop, then figure out how to make it not do that.

[Mr Larrington]

Frobbing the switch on the boiler timer to “permanently on” seems to do the necessary i.e. the heating comes on when:

• the thermostat timer says it's allowed to be on, AND
• the temperature in the Great Hall is below the limit

Only issue thus far is that a period of on-ness can’t be programmed to straddle midnight chiz.  This night wol wants the heating to be on approximately 09:00-11:30, 17:00-20-30 and 23:00-01:30.

[Tim Hall]

Do an early morning on ness from 0001 to 0130.  Assuming you don't run out of timing slots.

[Tim Hall]

Or set the time switch to Larrington time, which is two hours different to local time, so that 0130 local is 2330 Larrington Mean Time.

[Kim]

Frobbing the switch on the boiler timer to “permanently on” seems to do the necessary i.e. the heating comes on when:

• the thermostat timer says it's allowed to be on, AND
• the temperature in the Great Hall is below the limit

Only issue thus far is that a period of on-ness can’t be programmed to straddle midnight chiz.  This night wol wants the heating to be on approximately 09:00-11:30, 17:00-20-30 and 23:00-01:30.

Obviously the solution it to bodge it by telling it you're in the wrong timezone and offset the on/off times accordingly.  Because that's the sort of thing that will frustrate and befuddle whoever^[1] comes to jibble it in future.


ETA: Crosspost with Tim Hall by a matter of leap seconds.


_{[1] Probably you.}

[Mr Larrington]

Do an early morning on ness from 0001 to 0130.  Assuming you don't run out of timing slots.

Therein lies the promble.  Only four slots and it seems you can’t leave a gap between one ending and another starting chiz.  This is rather silly.