Nest Y plan (hot water turns heating on)

[Ricpat23]

Hi All,

New to the forum so hello and any help is appreciate.

Just installed my Nest 3rd gen on our Y plan heating system. I wanted to keep the thermostat in the same place so I decided to wire the heat link into the wiring centre (I’ll put a picture of wiring centre below before nest)

however I‘ve encountered a strange issue, the heating works perfectly on/ off etc but as soon as the ‘hot water’ turns on it also switches the heating on and the thermostat has no control over heating whilst hot water is on.

How I connected the heat link was;

L+2+5 = from fused 3a
Neutral = from wiring centre middle
wiring centre 8 to heatlink 4
wiring centre 9 to heatlink 3
wiring centre 10 to heatlink 6

in order to reuse thermostat wire I linked 2 & 3 and removed the black wires and placed these in T1 & T2.

as mentioned everything fired up and seemed okay until the hot water kicked in and overides it all.

as a note, the 3 port valve works fine as had to put system back to old style as needed hot water without heating. Plus I did leave the old programmer in situ while is did this and just turned both water and heating off.

I assume I’ve mixed up some cables somewhere so any help is appreciated.

 

[ianmcd]

Hi All,

New to the forum so hello and any help is appreciate.

Just installed my Nest 3rd gen on our Y plan heating system. I wanted to keep the thermostat in the same place so I decided to wire the heat link into the wiring centre (I’ll put a picture of wiring centre below before nest)

however I‘ve encountered a strange issue, the heating works perfectly on/ off etc but as soon as the ‘hot water’ turns on it also switches the heating on and the thermostat has no control over heating whilst hot water is on.


View attachment 323076
View attachment 323077

How I connected the heat link was;

L+2+5 = from fused 3a
Neutral = from wiring centre middle
wiring centre 8 to heatlink 4
wiring centre 9 to heatlink 3
wiring centre 10 to heatlink 6

in order to reuse thermostat wire I linked 2 & 3 and removed the black wires and placed these in T1 & T2.

as mentioned everything fired up and seemed okay until the hot water kicked in and overides it all.

as a note, the 3 port valve works fine as had to put system back to old style as needed hot water without heating. Plus I did leave the old programmer in situ while is did this and just turned both water and heating off.

I assume I’ve mixed up some cables somewhere so any help is appreciated.

For the mid position valve to work you must use terminal 5 on the heat link HW off

 

[RandomGrinch]

For the mid position valve to work you must use terminal 5 on the heat link HW off

Sorry Ian,
Terminal 5 is common.
Terminal 4 and 6 are HW N/C and N/O respectively.

How I connected the heat link was;

L+2+5 = from fused 3a
Neutral = from wiring centre middle
wiring centre 8 to heatlink 4
wiring centre 9 to heatlink 3
wiring centre 10 to heatlink 6

Could we have a picture of these connections as well, please?

 

[Ricpat23]

Hiya,

thank you for the responses.

please see pictures below. Please ignore the fact I used an earth cable for wiring.

 

[Ricpat23]

Sorry Ian,
Terminal 5 is common.
Terminal 4 and 6 are HW N/C and N/O respectively.


Could we have a picture of these connections as well, please?

sorry forgot to quote your post, pictures above.

 

[RandomGrinch]

sorry forgot to quote your post, pictures above.

Thanks, and I should have asked - a photo of the wiring centre, after the Nest install!

 

[Ricpat23]

Thanks, and I should have asked - a photo of the wiring centre, after the Nest install!

apologies I didn’t take any and had put the system back to normal (before nest).

just wired it again quickly to show;

 

[RandomGrinch]

just wired it again quickly to show

At a very (very!) quick glance, your wiring looks operative (excluding breaches of wiring regs, cable grips, oversleeving, Heat link requiring an earth when T1&T2 used, using green/yellow wire for a switched live etc... !).

To rule out a sticky relay on the Heat link, can you pull out and safely isolate the cable connected to terminal 3 of the HL, and see if the system goes to hot water only?