Replacing old dial thermostat (T630) with new digital

[dgsgc]

Hi all,
I have been trying to figure out if I can replace my current thermostat, which we are sure isn't working, with a new digital version.

This site has been loads of help over the last few months so thought someone may be able to help me.

We currently have the Honeywell T630 wired up with brown to 1 and blue to 3, picture attached. There is what looks like an earth as well, but this tucked away behind the back plate and I cant see if it is connected to anything.

After reading a few guides and loads of forum posts I am unsure if these are live and neutral or live and switched live.

Our boiler is a Main 30HE and has a small 24 hour mechanical dial controller, has little spiky bits that we switch for when we want the heating on, I'm sure you know I mean...

Can anyone help advise on what connections we have in the thermostat and what digital thermostat would be a good replacement, I don't want to buy one that's not compatible with the wiring set up.

Thanks
Dave

Untitled

• dgsgc
• 4 Feb 2014
• 1

 

[EFLImpudence]

The wires are obviously live and switched live.
The thermostat is just a switch.

What would happen if you connected live and neutral to a switch?

 

[jtonline]

...We currently have the Honeywell T630 wired up with brown to 1 and blue to 3, picture attached. There is what looks like an earth as well, but this tucked away behind the back plate and I cant see if it is connected to anything.

That looks like a T6360A(or B). According to the wiring diagram live comes in on terminal 1 and switched live goes out to the heating load on terminal 3. The thermostat is double insulated so doesn't need an earth connection, however if an earth wire is present it should be 'parked' on the earth terminal (furthest left) to comply with IEC guidelines.

...Can anyone help advise on what connections we have in the thermostat and what digital thermostat would be a good replacement...

Honeywell do a digital thermostat DT90, but I don't know if it would offer any major advantages over replacing your current thermostat with a new one of the same model (assuming your current thermostat is indeed faulty of course). Perhaps another forum user can advise on this point

Hope this helps,

 

[dgsgc]

Thanks guys.

The reason I was confused is that I kept reading about analogue dial thermostats having a neutral to power the small heating element that warms up the metal disc or something along those lines.

We would like to replace the old thermostat as we are sure it is not reading the temperature correctly and we would like a wireless programmable unit as our boiler control only has the 24 hour manual clock.

Am I correct in saying that we cannot use the wireless Honeywell CM927 as it needs a live and neutral and we do not have that. Is our only option the none wireless version that runs off batteries?

Also if this would work should we switch our boiler to on all the time and not use the manual timer clock and allow the new stat to control when heating is required?

Thanks again
Dave

 

[Whitespirit66]

That dial stat will work with 2 wires, but as you've discovered, not as well as with 3 wires. The anticipator won't be functioning.

As the Main has 230V switching, you can run a neutral wire to terminal 2 on the stat, which should make it work as intended.

Don't know why you would want the greater expense and arguably worse reliabilty of a wireless stat, when you have the wires in place to change to another wired stat if you really want to change. Of course, if you want to change stats position, that's another thing.

You can have a wireless stat if you want. You don't need a permanent 230V supply at the stat's location. Wireless stats have a receiver, which is normally installed near boiler, using boiler's 230V mains supply. The actual stat/transmitter is battery operated.

I would either run a neg. wire to existing stat, or replace with a battery operated wired stat that only needs the 2 wires you have at present.

 

[dgsgc]

Thanks very much. I think we will just go with the cm907 as that's a battery operated programmable stat like you suggested. We really would like the 7 programmeable feature but the wireless isn't really needed so no need for the extra hassle.

Can I just check that what I plan to do is correct.

Brown live on terminal 1 move to b on the cm907
Blue switched live on terminal 3 to a on the cm907

Cm907 manual- http://www.honeywelluk.com/Documents/Installation-Guide/pdf/1161.pdf

T6360 manual - http://www.honeywelluk.com/documents/Full-Specification/pdf/812.pdf

Is that correct?

Thanks for everyone's help.
Dave

 

[Whitespirit66]

Yes, those connections are correct. And, as you said in previous post, leave the boiler's manual timer switched on permanently and let new stat control timings for ch.

Good luck!

 

[dgsgc]

Excellent, thanks Whitespirit66. This site is great...

 

[jtonline]

Diagrams show brown to A, blue to B

 

[EFLImpudence]

It doesn't matter which way round in this case - just a switch.

 

[jtonline]

I know, but you may as well get it as per diagram

 

[dgsgc]

Thanks guys, could someone explain why it should be brown to A and blue to B, I cant see it from the 2 manuals and what I currently have. I am sure I am missing something but would like to understand it fully before I start.

What I see is current brown cable to terminal 1 is live on the T6360B, live is then terminal B on the new CM907. Current blue cable to terminal 3 on the T6360 which is switched live, this is terminal A on the new CM907.

Am I missing something?

Thanks
Dave

 

[EFLImpudence]

A and B are just connected when the thermostat is calling for heat (switched on) so it doesn't matter in your case which way round the wires are connected.

Different situations may mean you had to connect the live (brown) to A so that B or C would be live at different times.
Or even connect two supplies to B and C so that A is switched between the two.

The manufacturer is unlikely to draw two diagrams for your situation.


You could even argue that it is safer to connect the live to B so that terminal C is not live when the thermostat is not calling.

 

[jtonline]

Dave, just so you understand why I said what I did...

If you follow the black line from the L on the T6360 diagrams (that's your brown wire) it goes to terminal 1 on the diagram.

Now follow the black line from the L on the CM907 diagrams and it goes up to terminal A.

Follow the black line from terminal 3 on the T6360 and it goes to Heating Load (that's your blue wire). On the CM907 diagram the heating load line goes to terminal B.

But, as said, in this case either way around will work, I'm just of the opinion that if you follow the manufacturer's diagrams throughout an installation it makes subsequent work by anyone at a later date more straightforward as the connections match the diagrams in front of you.

I think you may have been confused by the fact that the manufacturer shows a switch in the live to the thermostat on the CM907 diagrams but has omitted it on the T6360 ones

 

[dgsgc]

Thanks guys, that does make sense now.