Nest 3rd Gen / Heat Link not Turning on Hot Water unless heating is on

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Felicity Hopkins

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Hi
We recently bought a new home that already had a Nest heat link and thermostat, which we have taken on.
Everything was working well and the system had learnt our schedule, giving us heating and hot water at certain times of the day.
Due to a kitchen refurbishment, we needed to move the heat link into the hall and ever since then we can't get hot water until the heating is switch on to manual. So we are either boiling hot (heating on) and have lovely hot water, or we are comfortable (heating off) but have freezing cold water.... please help us fix the problem....
The system is a Y plan configuration... if that helps?!
 

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Hello Felicity,

Who moved the heat link? It sounds like the heating call and hot water call have been swapped over. That or you have a motorised valve fault.
 
Hi CBW

our electrician moved the heat link and he’s cone back twice to look at it, but he’s not got the knowledge to know what is wrong.
from the photos I posted can you tell me how to check if the heating call and hot water call are swapped over?
Thanks
 
Sorry, not just by looking, unless they are a before and after? If they’re not before and after it just needs testing. If the wires were transferred exactly the same as before, then it’s a motorised valve fault.
 
Hi,

Only a DIY'er, so this may not be of any help!
But have you tried manually overriding the 3 port valve?
 
@RandomGrinch just wondering what your thinking is? When it's not powered, a 3 port valve sits in the 'hot water only' position already. Sliding the lever to MAN (Manual) moves it to the 'heating and hot water' position, (but usually not far enough to operate the switch that triggers the boiler) so I'm wondering what that would show? The OP says the HW works when the CH is on, it's 'HW only' that's the problem.

With the valve at rest and in the 'hot water only position' electrical control is limited to switching the boiler on and off, and that's done by the hot water cylinder thermostat via Heat link terminal 6.

Other than that; there are wires in the terminals that I would expect to see wires in for a Y-Plan (i.e. all of them except 1) and the links between L, 2 and 5 are present.

Unfortunately, unless you can tell us exactly what is connected to the other end of each of the wires after they leave the Heat link, it's going to be difficult to diagnose remotely over a forum, it really needs someone suitably skilled, with the appropriate test equipment to be physically present.

Bit of a longshot here, but was anything else changed or moved other than the Heat link being relocated? What happens if the HW is off and just the CH is on? does only the heating come on and work as it should?
 
stem said:
@RandomGrinch just wondering what your thinking is? When it's not powered, a 3 port valve sits in the 'hot water only' position already. Sliding the lever to MAN (Manual) moves it to the 'heating and hot water' position, (but usually not far enough to operate the switch that triggers the boiler) so I'm wondering what that would show? The OP says the HW works when the CH is on, it's 'HW only' that's the problem.
Click to expand...
Thank you, and please forgive my lack of knowledge of the 3 port valve. I didnt know that the manual position was unlikely to operate the switch. :oops:
My thinking was that, checking the position of the valve may help confirm if the heatlink is wired correctly.
And again this is something I don't know, but if the valve was at 'heating and hot water' position, can it be manually turned back to 'hot water only' to stop the OP overheating?
 
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