Replacing Honeywell ST699 Programmer with ST9400c

[clewis]

Hi, I recently replaced a 27 year old Honeywell ST699 Programmer with a new ST9400c. Whilst system delivers Heating and Hot Water, it will not deliver Hot Water when HW only is selected (despite green LED being illuminated) i.e. boiler does not fire. My wiring changes were as follows:

ST699 9400c

1 Live To L (Red)
2 N ——- N (Black)
3 ——— 4 (Red)
4 was empty
5 - 8 Link was discarded
L - 5 Link was discarded
6 ——- 3 (Yellow)
7 ——- 1 (Blue)
8 ——- 4 (Red)

I suspect that the Red wire from terminal 8 on ST699 to terminal 4 on ST9400c may be the problem, but not absolutely sure which terminal it should go to on 9400c. Can’t find on-line where to move Red wire at terminal 8 on St699. My system comprises 8 year old Bosch Worcester boiler, Drayton MA1 Mid level valve, new Honeywell DST90E room therm. Any advice would be appreciated.

 

[CBW]

Can you post a photo of the wiring? Visual is easier for me.

 

[ianmcd]

wire colours mean diddly squat on a heating system, as @CBW post a pic of what you have , and you dont have a mid level valve, no such beast exists

 

[denso13]

From one to the other,

 

[clewis]

Thank you CBW for responding. Photos of existing wiring on ST94000c and display with HW on ‘constant’ selected. Apologies, I meant Drayton Mid Motorised Position valve. Note: the numbered labels are as they were connected on ST966, with T8 connected to T4 on St9400c.

 

[denso13]

8 on the old one was a link wire and shouldn't be connected to the new one.

https://www.diynot.com/diy/threads/swapping-a-hw-st699-for-a-hw-st9400.503463/

 

[clewis]

Thank you denso13. I found this online, but it doesn’t tell you what to do with wire at old T8. I tried not connecting (isolating) the wire and not connecting to ST9400c, but then I couldn’t even get Central Heating (and no Hot Water)!

 

[clewis]

It seems the wire from T8 is doing something when connected to the new T4 as it allows the CH to function and I get some hot water even when HW is ‘Off’.

 

[Johnmdc]

The wire that was in 8 should be connected to L on your new clock.
(It was linked to L before by the links from L to 5 and 5 to 8.)

 

[clewis]

Thank you johnmdc. Can I confirm that this will give me two wires at Live on new programmer?

 

[Johnmdc]

Yes

 

[clewis]

johnmdc, that’s absolutely brilliant and thank you for your help. Everything is working correctly now. I can’t believe it was that simple.

 

[Johnmdc]

No problem

 

[wasjay]

Hi
Hopefully its ok to ask a question in this thread as i am also converting my old st699 to st9400c.
My question is, as we have had to move some appliances around the kitchen, the st699 is now awkwardly behind the fridge freezer.
So i will also need to move the programmer when i upgrade it, but im not sure what cable to use to extend the length.
Any advise please?

Many thanks