Honeywell ST699 to ST9400C Wiring Issues

[stem]

7 ---> 3
6 ---> 5
5 ---> Live

Based on the above wiring links and following the circuit through the switches shown on the ST699 diagram, it appears that you have an old system where the hot water is operated by gravity circulation and the heating by a pump. So whenever the boiler is on (for heating or hot water) the water gets hot by natural circulation of hot water rising up to the hot water cylinder. When the pump is started the radiators then heat up as well.

So this gives rise to an installation where the hot water setting controls the boiler, and the heating setting the pump. The problem is that for the heating to operate both settings have to be 'on' together so that both the boiler and the pump are running.

The above links ensure that whenever the pump is switched 'on' (for Heating) the boiler is also switched 'on' even if the hot water was set to be off.

The pump would have been wired to terminal 3, and the boiler terminal to 8

However, the ST9400C has a facility that is created by the links built in. So the pump would be wired to Heating ON and the Boiler to Hot Water on with it set to operate as a mini programmer using the special selection switch. Therefore any external links are not required.

With it set to Mini Programmer mode, the wiring for the ST9400C would be

N Neutral
L Live
1 Not used
2 Not used
3 Boiler Live (This was the wire in ST699 terminal 8.)
4 Pump Live (This was the wire in ST699 terminal 3.)

Some boilers, but not all also need a permanent live supply, so that's the wire shown dashed. If it was there before it needs to stay. Earths are omitted for clarity but should be maintained.

 

[ian1182]

Based on the above wiring configuration, you have an old system where the hot water is operated by gravity circulation and the heating by a pump. So whenever the boiler is on (for heating or hot water) the water gets hot by natural circulation of hot water rising. When the pump is started the radiators then heat up as well.

So this gives rise to an installation where the hot water setting controls the boiler, and the heating setting the pump. The problem is that for the heating to operate both settings have to be 'on' together so that both the boiler and the pump are running.

The above links ensure that whenever the pump is switched 'on' (for Heating) the boiler is also switched 'on' even if the hot water was set to be off.

The pump would have been wired to terminal 3, and the boiler terminal to 8

However, the ST9400C has a facility that is created by the links built in. So the pump would be wired to Heating ON and the Boiler to Hot Water on with it set to operate as a mini programmer using the special selection switch. Therefore any external links are not required.

View attachment 292570

With it set to Mini Programmer mode, the wiring for the ST9400C would be

N Neutral
L Live
1 Not used
2 Not used
3 Boiler Live (This was the wire in ST699 terminal 8.)
4 Pump Live (This was the wire in ST699 terminal 3.)

I agree with that. However the op said

N - Blue-A came from N
L - Brown-B came from L
1 - Brown-C came from 7
2 - Red-D came from 4
3 - Blue-E came from 6
4 - Blue-F came from 3

There was no connection in 8 on the ST699 unless they transposed 7 & 8 in their reply. Perhaps the #6 core is the boiler permanent live you mention above. Still no idea what the core in 4 (CH-Off) did. It's unfortunate no photo was taken of the ST699 prior to disconnection.

 

[stem]

The OP doesn't seem too sure, so what I've suggested is based on the wiring links that remain in the ST699. Follow the circuit through the switches and links and it becomes clear what they would do.

If there wasn't a connection to 8 then the main contact of the hot water switch wouldn't have been connected to anything, so rendering the hot water switch inoperative.

Maybe the hot water channel had broken and the boiler wire had been moved to 7. In which case 7 is linked to 3 which is the pump live, so the ST699 would have operated as a single channel, whereby the heating switch was the only one that operated, and switched everything on (boiler and pump) and the hot water channel did nothing. Just a guess, maybe the OP can confirm?

Or as you suggest it's because the OP transposed 7 & 8

Still no idea what the core in 4 (CH-Off) did. It's unfortunate no photo was taken of the ST699 prior to disconnection.

No neither have I, it's 'Heating NC' so would only be live (on) when the Heating was set to be off!

 

[SPayne]

Thanks fellas, as I said before, a proper schoolboy error in not taking a photo of the ST699 before disconnecting!! However, I have re-instated it so we got our heating back. I've confused issues a lot here by assuming the cable from the boiler was for the CH and the cable from the Pump was the HW, the other cable being the power. Intstead of checking where the cables came from, I've gone with the replacement wiring instructions as 3 into 4, 4 into 2, 6 into 3 and 7 into 1 and assumed the wires were originally in locations 3, 4, 6 & 7!! The thin red & blue cables you referred to Ian are the boiler. The fat brown and blue is the pump. The medium brown and blue is the power. So now I have the following connections which has put me back where I started:

8 - Live boiler
3 - Live pump
L - Live power
N - N boiler, N pump & N power
Then the links remain as they were in the pics 7-3, 6-5 and 5-L.

I've been doing a lot of Googling and Stem, you seem to have nailed it with the "Mini Programmer". There was no mention of this from Honeywell when I enquired, they just said it was a straight swap from the ST699 to the ST9400C, so I'm apportioning most of the confusion to them

I'm going to have a go at setting up this mini programmer later, I will keep you posted.

Thanks again for all your help, I've learned a lot

 

[ian1182]

Thanks fellas, as I said before, a proper schoolboy error in not taking a photo of the ST699 before disconnecting!! However, I have re-instated it so we got our heating back. I've confused issues a lot here by assuming the cable from the boiler was for the CH and the cable from the Pump was the HW, the other cable being the power. Intstead of checking where the cables came from, I've gone with the replacement wiring instructions as 3 into 4, 4 into 2, 6 into 3 and 7 into 1 and assumed the wires were originally in locations 3, 4, 6 & 7!! The thin red & blue cables you referred to Ian are the boiler. The fat brown and blue is the pump. The medium brown and blue is the power. So now I have the following connections which has put me back where I started:

8 - Live boiler
3 - Live pump
L - Live power
N - N boiler, N pump & N power
Then the links remain as they were in the pics 7-3, 6-5 and 5-L.

I've been doing a lot of Googling and Stem, you seem to have nailed it with the "Mini Programmer". There was no mention of this from Honeywell when I enquired, they just said it was a straight swap from the ST699 to the ST9400C, so I'm apportioning most of the confusion to them

I'm going to have a go at setting up this mini programmer later, I will keep you posted.

Thanks again for all your help, I've learned a lot

Excellent. You did originally say 7 rather than 8 which confused me. It makes more sense now. What has happened to the connections you indicated were in 4 and 6.

Now is a good time to take a picture of the status quo.

It looks like you do have a set of connections matching the PDF and that should make it easier to take the next step. It does not matter if multiple cores go into either/both of N & L as that's just the power side of things. What does matter are the cores in 3 thru 8 which support the switching

 

[SPayne]

Excellent. You did originally say 7 rather than 8 which confused me. It makes more sense now. What has happened to the connections you indicated were in 4 and 6.

Now is a good time to take a picture of the status quo.

It looks like you do have a set of connections matching the PDF and that should make it easier to take the next step. It does not matter if multiple cores go into either/both of N & L as that's just the power side of things. What does matter are the cores in 3 thru 8 which support the switching

They can't have been in 4 & 6 Ian, as I say, I just disconnected and assumed that's where they were based on the re-wiring instructions that came with the ST9400C.

 

[ian1182]

if you provide a picture of the current ST699 wiring we should be able to advise for the ST9400

 

[SPayne]

if you provide a picture of the current ST699 wiring we should be able to advise for the ST9400

I've put the cover back on now Ian, but it is as per the BASIC SYSTEM 1 you posted yesterday and as i have described above. I think I am going to go with what Stem posted and set it up as a mini programmer.