Programmer Horstman to Honeywell ST9400C

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I'm replacing Programmer Horstman H27XL with a Honeywell ST9400C but having problems with the wiring as the Horstman had 9 connectors and the Honeywell has only 7.

I've attached a photo of the Horstman wiring and a photo of how I've wired in the Honeywell.

I don't think it's heating the water

The central heating works

What have I done wrong?

I have an interconnecting loop over

Thanks
 

Attachments

  • Horstman.jpg
    Horstman.jpg
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  • Honeywell (1).jpg
    Honeywell (1).jpg
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Last edited:
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Thanks Chris,

I did as you said and now I've hot water but no central heating
 
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Is the heating still on and thermostat still calling for heat?
 
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The heating is still on and calling for heat.

The black wire is still in 4
 
Mmm. It should be - especially if nothing has changed regarding the black wire.

I can't help but think something else has 'turned off' the heating.
 
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Have you disturbed the black wire or has come loose? Photo of changed wiring please
 
The black wire is securely in place.

I've just put the wiring back as I had it originally in the photo, and as before, the central heating is working but not the hot water
 
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can you post a photo of the new wiring?
 
With the wiring as per the attached photo, the hot water heating doesn't work.

The central heating only runs if the hot water is selected to 'OFF'
 

Attachments

  • 20231219_205946.jpg
    20231219_205946.jpg
    198 KB · Views: 62
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Do you know what type of heating system you have?
Despite the modern wiring, might you have a Gravity system?
 
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