itsmedoofer
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Central Heating Thermostat

Fri Dec 01, 2017 11:47 am

Hi,

Anyone familiar with 3 wire central heating thermostats ?

I have a Honeywell T6360B that I am looking at replacing with a new Honeywell Lyric T6 (Wifi model), before starting I thought I would check my wiring.
Image

The diagram for the T6360 states:-

1 = Live
2 = Neutral
3 = Switched Live (Boiler Demand)
Earth

Putting a meter across the terminals I get the following.

With the thermostat down, no heating demand

1 – 2 = 5V
1 – 3 = 195V
2 – 3 = 250V

Thermostat up, heating demand…

1 – 2 = 250V
1 – 3 = 0V
2 – 3 = 250V

Do these results look correct ? I’m not sure, I think 1 & 3 may be incorrectly wired on the stat……

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DougieLawson
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Re: Central Heating Thermostat

Fri Dec 01, 2017 12:13 pm

Your "neutral" isn't neutral, it's switched live.

Beware 240V can kill, or burn your house down or both.
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itsmedoofer
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Re: Central Heating Thermostat

Fri Dec 01, 2017 12:27 pm

Thanks Dougie,

So you think 2 & 3 are swapped rather than 1 & 3 yea ?

I know, thats why I took a meter to it first :)

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DougieLawson
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Re: Central Heating Thermostat

Fri Dec 01, 2017 12:42 pm

Read the datasheet at http://www.honeywelluk.com/documents/In ... f/1151.pdf

Terminal#3 is switched live - the load is connected between it and the supply neutral.
Terminal#2 is the indicator lamp (shown with a resistor), that's lit when the stat is calling for heat.
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6by9
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Re: Central Heating Thermostat

Fri Dec 01, 2017 3:14 pm

Wow, there's off topic, and then there's off topic!

So based on the manual and diagrams, connection 1 should be live, 2 should be neutral, and 3 should be switched live to the boiler.
2 may not be connected in all installations - read about thermostat anticipators.

Taking your:
With the thermostat down, no heating demand
1 – 2 = 5V
1 – 3 = 195V
2 – 3 = 250V
I'd agree that 1 & 3 appear to be swapped. If wired correctly then 1 should be at 240V, 2 at 0V, and 3 at 0V. That's not what you've got. Your numbers are consistent with 3 being live, and 1 being switched live. The overall result would be that the system would work, but the anticipator will be doing nothing but burning a small amount electricity constantly.

Simplest test iff you consider yourself competent to work on mains is to power down, disconnect the wire on terminal 3, power up, and then measure again. If the now loose tail is live, you have your answer. The most useful tool for this is a mains test screwdriver as it'll tell you whether the terminal is live, rather than the respective voltage differences.


T6 installation manual, T6R installation manual
The Lyric T6 wants to put the receiver box where the current thermostat is, or it could be relocated to closer to the boiler/heating wiring centre. It's then a wireless connection from the stat to the receiver on the T6R, or 2 wires required on T6.

If you know where the other end of the wires currently at your thermostat are, then I'd site the receiver box at that other end, and use two cores of your 3core+earth cable to connect it to the thermostat in the current location. Make very sure of your connections first or things will let out the magic smoke.
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itsmedoofer
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Re: Central Heating Thermostat

Fri Dec 01, 2017 5:33 pm

HI 6by9,

Thanks for taking the time to reply !

LOL yea I suppose it is a fair way off the usual path..

Like I said I previously I thought I would check the existing wiring before I went too far, I had in my mind exactly that 1 at 250V and 2 & 3at 0V. When I saw the readings it threw me and made me start doubting myself.

I am going to take the existing stat off and put the base of the Lyric up that will let me terminate the wires and check a bit more easily, good tip about the mains test screwdriver, I have a multi-meter but not one of them, I'll pop up the hardware shop tomorrow.

I got the T6R in the sales last Friday, I'm going to struggle to get the receiver too close to the boiler, it's not bad looking, better than the T6360 so I don't mind it on the wall to be fair, it also has an override button so could be handy to have it in the open.

Again, many thanks !

itsmedoofer
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Re: Central Heating Thermostat

Fri Dec 01, 2017 7:45 pm

Hi 6by9,

Thanks again for the confirmation, all working properly now. As confirmed live and switched live were swapped.

Got it connected to the Echo so can use that as well, well cool :)

Me.

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