Central heating thermostate

Joined
14 Nov 2013
Messages
66
Reaction score
6
Location
Deal , Kent
Country
United Kingdom
Hi All,

Perhaps someone can help.

Our existing central heating thermostat (not programmable) is an old Honeywell dial type with 4 wires going to it (earth-blue-yellow-red) I have just bought a new digital one, the same make & size to replace it. I thought I would be able to fit it by fitting the 4 wires to the same terminals on the new one.

The problem is the new one only needs 2 wires, looks like live & neutral no earth. I would be grateful if somebody could confirm that I would only use the live (red) & neutral (blue) & then blank off the 2 remaining wires.

Thanks for any help.
 
Sponsored Links
It's more likely you need live and switched live. But it's hard to say without knowing more details.

Does the new one use batteries ?

What were the labels on the terminals that each colour went to on the old one?

As a guess, I would say you need the red (live) and yellow (switched live) for the new one, but that is purely a guess with the information at hand.
 
I would be grateful if somebody could confirm that I would only use the live (red) & neutral (blue) & then blank off the 2 remaining wires.

.

If you do that then you will probably blow your new stat.

1. Never assume that a blue or black wire is a neutral. Its just a blue or black wire. Electricity does not understand colours and plumbers especially do not.

2. Make a careful note of what wires go where on the existing stat BEFORE YOU TAKE THEM OFF.

3. Read the DIYNOT WIKI that tells you exactly what to do. //www.diynot.com/wiki/electrics:how_to_replace_a_room_stat

4. Come back and tell us if you have problems, or if you succeed.
 
I would agree for any thermostat to work it must have live and switched live connected. As to which colours they are you need to look at old one. Depending on room put earth and neutral into connector block or tape up I would not cut them as may be required in future.
 
Sponsored Links
Thanks for the replies. The new one does need batteries.

I will have to check back later to read the suggested links.

Thanks again.
 
If it is battery powered, it does not need the neutral. It will need a live feed and then a switched live back to the boiler, but as has been said, their is no guarantee which colours are doing what. Terminate the neutral safely and tuck it out of the way. If there is a metal back box, connect the earth to that.

As far as the boiler knows, the thermostat is just a switch and the boiler will respond to the presence, or not, of a live at its internal controller. But you need to know for certain which wire that is. You could look at the boiler end for wire colours, but there is no guarantee that even they are the same at both ends, it may all go into a junction box somewhere where colours may change.
 
As far as the boiler knows, the thermostat is just a switch and the boiler will respond to the presence, or not, of a live at its internal controller. But you need to know for certain which wire that is. You could look at the boiler end for wire colours, but there is no guarantee that even they are the same at both ends, it may all go into a junction box somewhere where colours may change.

He should be able to determine N, L and SL just from where they are connected to the old 'stat. No need to disturb anything else.
 
As far as the boiler knows, the thermostat is just a switch and the boiler will respond to the presence, or not, of a live at its internal controller. But you need to know for certain which wire that is. You could look at the boiler end for wire colours, but there is no guarantee that even they are the same at both ends, it may all go into a junction box somewhere where colours may change.

He should be able to determine N, L and SL just from where they are connected to the old 'stat. No need to disturb anything else.

My bad, I was under the impression the old stat was already taken off.
 
Have you read the instructions that came with the new stat? Usually they have charts of various makes of stat showing how the old wiring relates to the new one.

PJ
 
Hi All,

I would like to thank all of you who posted replies to this post.

However I do not have the confidence to do this myself so I feel it would be better to leave well alone & to seek the help of an electrician.

Thank you once again.

Brian.
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Back
Top