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View the thread, titled "hot water won't turn off" which is posted in Central Heating Forum on UK Plumbers Forums.

I disconnected the orange wire and turned the power on. The MV still moved around and engaged the switch but the boiler didn’t fire up (I guess that’s what the orange wire does 🙂)

Good to see problem solved by removing the permanently live grey wire from terminal 8, think I have seen something like this on a outside grant boiler where the frost stat was incorporated in here, it may be worth tracing this wire sometime especially before winter sets in especially if you have a outside boiler, also would be interesting to see where the ufh is controlled from sometime.
 
Good to see problem solved by removing the permanently live grey wire from terminal 8, think I have seen something like this on a outside grant boiler where the frost stat was incorporated in here, it may be worth tracing this wire sometime especially before winter sets in especially if you have a outside boiler, also would be interesting to see where the ufh is controlled from sometime.
The UFH set up is in the pictures. The MV is on the pipe straight out of the boiler to the right. The controls are just above the boiler to the right. The UFH controls were just added to the CH controls that were already there. I am pretty sure something is wrong with this setup, nothing has been as it should since it was installed.
I have highlighted where the wire from upstairs that I disconnected goes on the frost stat
I have no idea what will happen come winter with the wire that I disconnected - or even it will have any affect on anything?
 

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There also seems to be a brown wire in terminal 3 of the frost stat as well as the grey wire which presumably should be a switched live, wonder if that brown is the permanent live and should be somewhere else?.
 
Yep looks like a frost stat issue looks like 3 wires into terminal 3 when there should be one

They’ve buggered the wiring up when they’ve added the extra 2 port /ufh
 
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There also seems to be a brown wire in terminal 3 of the frost stat as well as the grey wire which presumably should be a switched live, wonder if that brown is the permanent live and should be somewhere else?.
The grey cable in terminal 3 is to the MV of the UFH. It also has a black cable from the cable coming from upstairs and the brown wire from the MV control box. The permanent live from upstairs that is disconnected is in the blank terminal to the right of terminal 4.
 
Could you run a new wire from the ufh manifold to upstairs where the wiring centre is ?
 
The grey cable in terminal 3 is to the MV of the UFH. It also has a black cable from the cable coming from upstairs and the brown wire from the MV control box. The permanent live from upstairs that is disconnected is in the blank terminal to the right of terminal 4.
What is the stat's make/model?
 

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