Nest gen 3 - Y plan - fitted but heating will not switch off

[md45]

Hi everyone,

So after reading the many other threads about problems with the nest, i cant find any issues which match mine.

I'm pretty sure i have a Y plan system and that i have wired the Nest correctly, after wiring it in the heating and hot water all come on but the heating will not switch off regardless of what i do with the nest thermostat, the only way i can switch it off is buy switching off the main power to the heatlink.

My system consists of the following

A boiler in the kitchen with the old mechanical programmer next to it
A water tank upstairs with one valve, a pump, a cylinder thermostat and a room stat wired into the wiring center which is in the cupboard with the water tank

I have left my old wired thermostat in place and switched it fully on.

I've attached some photos, I feel like iv'e come as far as i can with my limited knowledge of these things and would really appreciate help from someone, I accept that any damage/wrong wiring is completely my responsibility

 

[stem]

I assume that the Heatlink has replaced the old mechanical programmer. If so, then the wiring appears to have been transferred over OK. Did you change anything anywhere else?

Although it won't cause the problem, the wiring could do with tidying up a bit though, there shouldn't be all that copper on show out of terminals 4 & 6. They should look like the original installation, just the tiniest bit of copper visible, the loop between 2 and 5 should remain inside the enclosure. Also, the cable outer sheaths should be secured under the cable clamps, and not the wires. But we'll put that down to it being a work in progress

Whilst you were installing it, did you inadvertently create a short circuit, or blow a fuse at any time?

Odd that someone else has also reported a similar thing.

 

[md45]

Hi Stem

Thanks for the reply,

Yes the heatlink has replaced the old programmer.
the two wires coming out of terminal 2 are both loops, one leads to live and one leads to terminal 5 (sorry the image isn't very clear)

The wires were fitted better than that (honest!) i took the picture just as i was in the process of removing the heat link and putting my old system back together..


I've removed and replaced the heatlink 3 times now and each time i put the old system back together it works as it should, When i put the nest system on the heating comes on and stays on regardless of what i do with the nest thermostat, when i turn the thermostat i can hear the switches working in the heatlink but they dont have any effect on actually turning the heat off, after spending hours researching and checking wiring diagrams i cant find anything wrong with the wiring..

One thing to note with my current thermostat is that i can either have the heating and hot water on together or just the hot water on, it wont let me put the heating on by itself unless i press the boost button..

Just to clarify there isn't a fault with the current programmer, there are two sliding switches, one for water, one for heating, there are three options on each switch, 'twice', 'on' & off, if i attempt to slide the heating switch to on then the water switch comes along with it even though i'm not touching it,

Hope this makes sense!!

Thanks

 

[Wildcat1961]

Perhaps call someone who knows what they are doing.
Every man and his dog seem to be fitting nest.

 

[md45]

wildcat 1961 - thank you very much for your helpful input

 

[md45]

Stem, I haven't changed anything else and haven't blown any fuses, when i put the old system back together and remove the nest it works fine, ive only ever wired it as per the picture and instructions so im thinking it cant be down to me doing anything wrong and can only be a fault with the nest.... Thought i would let someone like yourself cast your eye over things first though just incase you cold spot something obviously wrong..

If you think it looks as it should then i will either return this nest (if i can) and buy another one with fitting, or get someone to come and fit this one just to see if they can either confirm that the nest is faulty or that something needs to be adjusted with my existing system

i've emailed nest and they say 'there is a possibility that the valve is stuck on ON mode (heating on) and therefore it was not switching OFF the heating'.. Any thoughts on that?

Thanks

 

[stem]

The actual connections seem to be in the right places

A sticking valve is possible, and it does happen occasionally, but it's rather coincidental don't you think? Assuming of course that it was working OK before.

It's quite easy to see if the Heatlink is the problem. Remove the yellow wire from terminal 3 and then try it. If the heating comes on now, then the problem is elsewhere in your system, if it doesn't come on with the wire removed, it's the Heatlink that is keeping it switched on.

 

[md45]

Stem, thanks for taking the time to give your advice, to have someone in the know give their opinion is a massive help especially for someone like myself who has hit a wall and doesn't have the knowledge to investigate the problem, so i decided to contact a 'nestpro' and one of them came out to me, he checked the heatlink unit and confirmed that it was at fault, (regardless of whether the heating was on or off the heatlink was still putting a live feed out).. Nest have asked for a report from the nest pro which ive now sent to them.... I'l update the post on what happens next....