Programmer Horstman to Honeywell ST9400C

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'
I can’t help but notice you have tightened the screws onto the insulation, maybe try (humour me) just the terminal tabs onto the conductor.

I also take it that it worked ok, as in independently on the Horstmann?
 
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I can’t help but notice you have tightened the screws onto the insulation, maybe try (humour me) just the terminal tabs onto the conductor.
Sorry, I don't understand what you want me yo do. Okay, I think I do - the insulation on the wires is what you mean

Usually it would work without a problem, but there was an intermittent fault with the Horstman - the central heating would work only when the hot water was turned 'ON' - The reason for changing the controller
 
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A gravity system
The Horstmann had a specific setting to allow for a Gravity system; it would transparently switch the hot water on when there was a C/H call-for-heat.

The ST9400C, doesn't have this - but it does have a 'Mini programmer" mode...

Screenshot_20231219-220727_Adobe Acrobat.jpg


If you want to retain transparent operation, alternatives, such as a Hive, do have a gravity mode.
Or, for a gain in efficiency, it be worth looking to update your heating system with some valves?

In the mean time, if you wish to stick with the ST9400C, put the grey wire in terminal 3, the black wire in terminal 4 and put in a programme for hot water and one for heating to run concurrently, whenever you need C/H.
 
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I've adjusted the wires so that the screws turn into the bare wire.

At the moment with the wiring as requested, the hot water works but the central heating doesn't work at all.

I'm off to bed now

Thanks
 
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Good Morning.

As requested
 

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Doesn’t appear to be gravity. Definitely something knocking heating off. Can you post a photo of the cylinder cupboard
 
A gravity system
Just a caution with the term 'gravity'. In reference to heating controls it refers to a system where only the central heating is pumped and the hot water cylinder is heated naturally by 'gravity circulation' i.e. water circulates naturally between the boiler and hot water cylinder, in that hot water rises and cooler water sinks it's not pumped. Some think that gravity purely means having cold water storage tanks in the loft, but it doesn't.

Just wondering why you are replacing the Horstmann. Was there a malfunction you were trying to rectify?

When you try the heating and it doesn't come on, is the room thermostat actually calling for heat, in this unusually mild weather, it might not be.
 
Just wondering why you are replacing the Horstmann. Was there a malfunction you were trying to rectify?
Usually it would work without a problem, but there was an intermittent fault with the Horstman - the central heating would work only when the hot water was turned 'ON' - The reason for changing the controller
 
Just a caution with the term 'gravity'. In reference to heating controls it refers to a system where only the central heating is pumped and the hot water cylinder is heated naturally by 'gravity circulation' i.e. water circulates naturally between the boiler and hot water cylinder, in that hot water rises and cooler water sinks it's not pumped. Some think that gravity purely means having cold water storage tanks in the loft, but it doesn't.
Sorry. In that case it is pumped, not gravity
 
Usually it would work without a problem, but there was an intermittent fault with the Horstman - the central heating would work only when the hot water was turned 'ON' - The reason for changing the controller
Hmm....Sort of similar with the Honeywell, so looks like the problem may well be elsewhere.
 
Usually it would work without a problem, but there was an intermittent fault with the Horstman - the central heating would work only when the hot water was turned 'ON'
Hmm....Sort of similar with the Honeywell, so looks like the problem may well be elsewhere.
Exactly the same by the looks of it!

I was wondering why the C/H came on when the OP had wired Grey to the N/C terminal 1.
Power was provided to both grey and black, hence my thoughts on 'Gravity'.
 
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'

1703078847682.png


I don't suppose the Grey and Black are the wrong way round are they?

That is:
Grey is Central Heating
and
Black is Hot Water.
 
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I don't suppose the Grey and Black are the wrong way round are they?

I've changed them around as suggested.

The Central Heating works.

The Hot Water appears to work, (pipes are hot), but the pump doesn't come on as it did with the Horstmann

I'll check on it later.

Thanks
 
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