3rd Gen Nest - Hot Water only works when Central Heating is on

[uptoyou]

Hi all,

Took a few days to catch this as timings of household activities hid the problem.
Having installed a Nest a week ago, I have now discovered that the H/W is only working when the heating comes on (it is on a schedule to be on all through the day but it just doesn't come on).

'Boost' on the Nest display will light up as if it is working when pressed, but only when I turn the thermostat up will it work - this is based on the boiler firing up when I up the temperature, and 30 mins later I start getting hot water form the taps.

If the thermostat is not turned up to fire the boiler, the 'Boost' will not do it itself.
We never had any issues with our last setup (Drayton/Honeywell Wireless), so assume it must be a Nest setting/wiring issues?

I will get the wiring diagram up shortly, but on the meantime does this issue spring to mind as being anything specific?

 

[muggles]

Definitely sounds like it's been wired incorrectly

 

[ianmcd]

need more info S plan ? Y plan? cyl stat? pics of wiring, most so at the nest sounds like you have missed something

 

[uptoyou]

Thanks both, ianmcd - you responded on my original 'sanity check' post, so this is a week or so in since that thread.

Boiler - Worcester Greenstar ri, Y-Plan I believe, before and after below:

 

[picasso]

Why do you have heating on (3 on nest) going to the cylinder stat and hot water on bypassing the cylinder stat completely ?

 

[Johnmdc]

As Picasso suggests you have got 3 and 6 on the nest the wrong way round.

 

[uptoyou]

Thanks both, I haven't changed any module wiring, so have I misinterpreted the instructions to directly replace the the wires from the LP522 to the HeatLink, I have followed the below:

LP522 N = Heatlink N
LP522 L = Heatlink L
LP522 1 HW off = Heatlink 4 Hot Water Satisfied
LP522 2 CH off = Heatlink 1 Heating Satisfied
LP522 3 HW on = Heatlink 6 Hot Water Call for Heat
LP522 4 CH on = Heatlink 3 Heating Call for Heat

There was one forced change in the wiring whereby once I removed the old wireless hub:
- I was left with a spare wire (yellow in the diagram), coming from the motorised valve which was going originally to a switch on the wireless hub.
- A spare wire, originally Pin 3 (call for HW), on the LP522, now Pin 6 ( HW call for heat), on the HeatLink

As the motorised valve wire was originally going to the wireless hub switch, activating 'Heating On' on the old programmer, this looked to me like connecting them together would allow the HeatLink to control the switching?

 

[picasso]

Both of the diagrams are wrong, I would suggest you rewire from scratch using the nest y plan diagram.

 

[ianmcd]

why did your LP522 have a CH off wire ? it is not needed

 

[uptoyou]

why did your LP522 have a CH off wire ? it is not needed

Hi iancd, if 'CH off' on the LP522 is pin.2, then it doesn't have a wire, and pin.1 is not used on HeatLink either.

 

[uptoyou]

Both of the diagrams are wrong, I would suggest you rewire from scratch using the nest y plan diagram.

Hi picasso, can you elaborate what is wrong on the first diagram, as this is the exact wiring before I replaced it for the Nest?

@Johnmdc - should switching those two wires fix this?

 

[Johnmdc]

If it is wired like your second diagram then yes change the wires in 3 and 6 around. That should cure it.

 

[picasso]

You have the grey wire from 3 (hw on) going to the bdr and the black wire from 4 (ch on) going to the cylinder stat.

 

[uptoyou]

Thanks everyone, switching 3 & 6 around looks like it has solved it, I'll see how it performs over the next couple of days!

 

[ianmcd]

Thanks both, I haven't changed any module wiring, so have I misinterpreted the instructions to directly replace the the wires from the LP522 to the HeatLink, I have followed the below:

LP522 N = Heatlink N
LP522 L = Heatlink L
LP522 1 HW off = Heatlink 4 Hot Water Satisfied
LP522 2 CH off = Heatlink 1 Heating Satisfied
LP522 3 HW on = Heatlink 6 Hot Water Call for Heat
LP522 4 CH on = Heatlink 3 Heating Call for Heat

There was one forced change in the wiring whereby once I removed the old wireless hub:
- I was left with a spare wire (yellow in the diagram), coming from the motorised valve which was going originally to a switch on the wireless hub.
- A spare wire, originally Pin 3 (call for HW), on the LP522, now Pin 6 ( HW call for heat), on the HeatLink

As the motorised valve wire was originally going to the wireless hub switch, activating 'Heating On' on the old programmer, this looked to me like connecting them together would allow the HeatLink to control the switching?

LP522 2 CH off = Heatlink 1 satisfied

Hi iancd, if 'CH off' on the LP522 is pin.2, then it doesn't have a wire, and pin.1 is not used on HeatLink either.

and you posted this , are we supposed to just guess ?