Thermostat wiring confusion

[kylescudder]

Hi all,

I became a home owner in March of this year, and after a manic rest of the year I am just starting to get around to some DIY bits and pieces.

One of the things on my to do list is replace the old Honeywell ST9100A unit with something like a Hive or Nest replacement.

From what I have read so far, the multiple wires into earth, neutral and live, I just need to make sure they all go into the corresponding terminals on the new controller, same with 1 and 4. People have suggested that 1 goes to 1 and 4 goes to 3, so that part seems straight forward enough. The thing that I am unsure of is the cable going into 1, is just bridged from live.
Is this okay and safe to do, and if I was migrating to another system, would the same solution be okay do so, or should I be considering alternative options?

Thank you for any help in advance.

 

[Titch2k6]

Hi Kylescudder,

This has been covered before on the forums. An old post, but I think you can find the information you want here.

Regards

 

[CBW]

Yes, the link/bridge is for a common supply, often, but not always needed in a new programmer setup, just read the instructions to ascertain if required. A word of warning, a blue wire has been used for a switch live, which is perfectly acceptable, however do not confuse this for a neutral wire.

 

[Adam_151]

Looking at installaiton isntructions online: It would seem that 1 as common and 3 for N/O would be right for a hive but...

on the nest it seems that for the heating relay: 2 is the common and 3 is the N/O. Don't need 1 as thats N/C
4/5/6 also not relevant if installing it here as they are for the DHW relay - What sort of boiler/heating system do you have?
Do you have any other control devices other than this? Presume there might be a separate wall stat somewhere?

Loop the common off the Live like it is currently

 

[ericmark]

The same wall plate

can be wired different depending if one, two or three channel, the ST9100A

is a programmer rather than a thermostat, one would expect to find it used with a thermostat

and thermostat will need removing in most cases.

The first job is sit back and work out what you want as the final result. Then decide which step will come first, I will admit I made an error, I read all the adverts as to what could do what, and thought Energenie TRV heads would work with Nest, it was wrong, however you still need to work out what the final result is that you are aiming for.

I use a collection of TRV heads, and they all work to an extent. No wiring involved just unscrew one head and replace with another. But on their own the TRV heads can't turn the whole boiler on/off, but how far you go is up to you.

Big question is what do you have now, no good talking about opentherm if your boiler is not enabled.

 

[kylescudder]

The same wall plate View attachment 322188 can be wired different depending if one, two or three channel, the ST9100A View attachment 322189 is a programmer rather than a thermostat, one would expect to find it used with a thermostat View attachment 322190and thermostat will need removing in most cases.

The first job is sit back and work out what you want as the final result. Then decide which step will come first, I will admit I made an error, I read all the adverts as to what could do what, and thought Energenie TRV heads would work with Nest, it was wrong, however you still need to work out what the final result is that you are aiming for.

I use a collection of TRV heads, and they all work to an extent. No wiring involved just unscrew one head and replace with another. But on their own the TRV heads can't turn the whole boiler on/off, but how far you go is up to you.

Big question is what do you have now, no good talking about opentherm if your boiler is not enabled.

Thank you for taking the time to reply.
The boiler is a Worcester Greenstar 4000 25kW Combi NG.

 

[ericmark]

Thank you for taking the time to reply.
The boiler is a Worcester Greenstar 4000 25kW Combi NG.

I am not a plumber or heating engineer, just an electrician, but seem to remember Worcester never sighed up to OpenTherm and boiler modulated in the main on the temperature of the return water, so TRV's and the by-pass valve is the main control tools. Having a well thermostat correctly set can reduce boiler cycling, and if linked to the TRV can ensure the boiler turns on when required, but you could also use manual control of the boiler.

So the likes of Wiser or Evohome (Drayton or Honeywell) will ensure the system works in the most efficient way, but a cheap £35 wall thermostat and £15 programmable heads for the TRV's if the lock shields are correctly set can get near the same results, as to how near depends on your house, but the big decision is how far to take the control? The all work, but some work better than others, it may well be you can go half way, with some linked TRV heads and some stand alone.

But the TRV is king, and the Wiser TRV head is claimed to work out how long it takes to heat the room, so turns on a varying time before the time set to ensure room to temperature at the time set. Mine are far simpler, but only you can balance the install cost to comfort and running cost. Much will depend on home size and your life style, since I am retired I don't need geofencing etc, you may need it, so only you can decide the route to go down.

However fitting a new programmable TRV head is far easier than wiring a wall thermostat. So it would seem getting TRV heads then a wall thermostat that will work with them is the logical route.

 

[kylescudder]

Looking at installaiton isntructions online: It would seem that 1 as common and 3 for N/O would be right for a hive but...

on the nest it seems that for the heating relay: 2 is the common and 3 is the N/O. Don't need 1 as thats N/C
4/5/6 also not relevant if installing it here as they are for the DHW relay - What sort of boiler/heating system do you have?
Do you have any other control devices other than this? Presume there might be a separate wall stat somewhere?

Loop the common off the Live like it is currently

Thank you for taking the time to reply.
The boiler is a Worcester Greenstar 4000 25kW Combi NG.

So if I want to move 4 to 3, this being the hearing call for heat N/O, and of course move N, L and earth, that would work? Or do I need to loop 1 from L to anything in the Nest thermostat?

 

[Adam_151]

The boiler is a Worcester Greenstar 4000 25kW Combi NG.
So if I want to move 4 to 3, this being the hearing call for heat N/O, and of course move N, L and earth, that would work? Or do I need to loop 1 from L to anything in the Nest thermostat?

Combi Boiler - So don't need to worry bout the hot water relay.

So you have any other control devices apart from that unit you have removed, a separate wall stat anywhere because it looks like you have a cable that has a core connected to 4, and another core to that connector block?

If so, you could tidy it up by removing that, and likely even re use the cable to provide the extra low voltage supply from the heatlink to the next itself

But if you were doing a like for like swap. You'd want to put whats in 1 (the link to the Live) into 2 on the nest heatlink. And what is in 4 now goes to 3 on the nest (that blue wire with brown sleeving)

 

[kylescudder]

Combi Boiler - So don't need to worry bout the hot water relay.

So you have any other control devices apart from that unit you have removed, a separate wall stat anywhere because it looks like you have a cable that has a core connected to 4, and another core to that connector block?

If so, you could tidy it up by removing that, and likely even re use the cable to provide the extra low voltage supply from the heatlink to the next itself

But if you were doing a like for like swap. You'd want to put whats in 1 (the link to the Live) into 2 on the nest heatlink. And what is in 4 now goes to 3 on the nest (that blue wire with brown sleeving)

You are honestly so helpful for this, thank you so much.

I have a wall thermostat that I will be replacing with the Nest Learning Thermostat. I have not taken that off the wall yet to see what cables are a part of that, I wanted to get the Heat Link sorted first.

I think for now I would like to do a like for like swap, and then when my electrician mate comes over in a few weeks, get him to sign it off and make sure it is all correct. If at that point he decides that removing and tidy it up is the best thing to do, then we can do that then.

Thank you again, will let you know how it goes!