Honeywell ST9100C programmer/thermostat wiring problems

[Kingbroady]

I asked an electrician that I’d employed to disconnect the central heating timer from the thermostat. The reason was that TWO Honeywell ST9100C programmers had stopped working after he wired it separately from the plumber installing the new central heating system. Therefore:

A. Is there some way that I can check that it is wired correctly as I don’t trust the electrician now after two have stopped working for no apparent reason. I asked him to check it and he said it was fine.

B. How do I reconnect the programmer to the thermostat, please? I’ve attached photos of how it is at the moment.

Untitled

• Kingbroady
• 11 Feb 2013
• 1

Untitled

• Kingbroady
• 11 Feb 2013
• 1

Thank-you in advance.

 

[stem]

The wire that provides the live supply to the thermostat should be connected to terminal 4 of the programmer.

At the moment it looks to be connected to terminal 1 at the programmer. If so, this means that it will be permanently live and not switched on or off by the programmer. If you can determine that this is the case. Then move the wire at the programmer from terminal 1 to terminal 4. (Leave the loop between L & 1 in place.)

 

[RF Lighting]

Are you sure he was an electrician? That work doesn't look like it's been done by a competent electrician.

However, there is nothing there which would cause the programmers to fail.

To re-engage the programmer, with the power isolated, you need to move the grey wire which is in terminal 1 over to terminal 4, and then re-fit a programmer.

 

[Kingbroady]

Thanks. I'll give it a try.

Yes, he's registered with NICEIC. I checked their website and despite my sweating, he appeared on the last page for that region.

I'll give it a go and let you know.

Thanks both for your help.

 

[Kingbroady]

 

[Kingbroady]

Hi.

Issue was resolved; however, a new issue.

The central heating would not switch on via the programmer. However, we still had hot water. A central heating engineer attended and linked this out in the boiler so we could use the central heating.

I've bought a new programmer (exactly the same as before Honeywell ST9100C). How is it to be reconnected at the boiler, please?

 

[stem]

The ST9100 is wired as below

Remove the black/white wire link between boiler terminals 3 & 4 that was installed by the heating engineer

ST9100 'N' goes to the boiler 'N'
ST9100 'L' goes to the boiler 'L'

ST9100 '1' goes to the boiler '3'
ST9100 '4' goes to the boiler '4'

 

[Kingbroady]

Thank you.

So the only connections to now make are in the boiler; terminals 3 and 4.

Terminal 1 of the programmer is the brown live so will go into terminal 3 of the boiler.

Terminal 4 of the programmer is a light grey. The flex in the boiler to connect has 4 cores; black, brown, dark grey/blue and the earth. Would I connect the black or grey/blue core, please?

 

[stem]

OK, so there is some existing wiring in place that may need further investigation. The advice I gave in my first post was based on starting from scratch.

There are several ways to wire up these things, so I will need to know where all of the existing wires in the photo go, particularly the brown wire from the room thermostat terminal 3.

EDIT
Also the specific model number of your boiler. I can tell it's a Vaillant, but there are sometimes slight differences as the product evolves and between variants.

 

[stem]

I have had a bit more time to study your photographs now and have worked out the following diagram which I think represents how your system is wired. Please check that the wires are as I have sketched and go where shown.

I also believe that you have an ecoTECH Combi boiler as the terminals shown in the Vaillant manual below matches your photo. If you have a different boiler please advise.

At the boiler end you will still need to remove the loop between terminals 3 & 4, but wiring it as I have shown in my sketch means that you will not need any connection to the boiler terminal 3.

The brown wire in my sketch from the thermostat terminal 3 which should go to the boiler terminal 4 will have been disconnected, when the loop between 3 & 4 was added

If anything is different to what I have shown or said above, or you are unsure about anything check first.

EDIT
Replaced original black / white scruffy hand drawn sketch with proper drawing. No changes made to the wiring connections.

 

[Wildcat1961]

At the boiler end you will still need to remove the loop between terminals 3 & 4, but wiring it as I have shown in my sketch means that you will not need any connection to the boiler terminal 3.

Using terminal 3 will ensure all voltage to boiler is interrupted via boiler spur.

 

[Kingbroady]

Thank you both. The model is a Vaillant ecoTEC pro 28.

 

[Kingbroady]

Thank you. I've followed your advice; however, the boiler still fails to operate the central heating with a new programmer added. Could it be the thermostat?

 

[stem]

First of all check the wiring connections carefully. Especially the brown wire going to the boiler. It should be in terminal 4 as per my drawing, and not in terminal 3.

Secondly, if the brown wire was in terminal 4 already, does the Honeywell ST9100C power up OK?

If it does power up OK, does the green indicator lamp between the 'extra hour' and 'override' buttons illuminate when the heating is switched on?

If it the green light does come on, the next test would involve inserting a loop wire (you can use the black / white one you have just removed from the boiler) and join the programmer terminals 1 and 4 together. Leave the other wires in place. Don't replace the programmer on the backplate and try it now. If the boiler operates now, the programmer is faulty.

 

[Kingbroady]

Thanks.

I checked and the wire is correctly in terminal 4 of the boiler. However, on testing it with a Fluke VoltAlert, it indicated no current.

The new programmer powers up, clicks and lights up as it should and as the previous one did. However, the central heating still doesn't switch on.

I have linked terminals 1 and 4 of the programmer backplate but still the central heating fails to operate.