ST7100 - CH Wiring Query

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Hi,
Have switched our hot water and central heating to our summer settings using Honeywell ST7100 and have found that the central heating is still coming on despite having set all settings instances not to. Effectively the central heating is coming on at the same time as the hot water is set to.
I've checked the user guide and the ST7100 Internal Switching Arrangement on page 12 appears to indicate that the unit has been incorrectly wired which is resulting in the above-mentioned issue. I've attached a photo of the unit with the cover removed for reference.
There is no wire connected to the CH Off terminal. Can anyone advise how I should go about fixing this?
 

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CBW

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Looks like you have a 3 port mid position valve, which sounds like it’s stuck in mid position, thus, bringing your heating on.
 
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Hi Chris,
Thanks for your reply. Do I therefore take it that ST7100 does not require a wire connected to the CH Off terminal in order to control the central heating?
 
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CH off is hardly ever used on any heating set up, it is used on commerciall installations where they have air conditioning, but hardly ever on a domestic installation
 
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sounds like the motor on the 3 port valve has failed, that would be my first check
 
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