Defective Nest Heat Link?

[dilalio]

Just wired up today.
Couldn't get hot water to turn off unless using cylinder stat.
Constant 240v on pin 6 of heat link despite no demand on stat.
Linked 240v over from L pin to pin 2 (CH) and pin 5 (HW).
Guessing relay stuck on HW.

Sanity check please.

 

[ianmcd]

which boiler ? S plan or Y plan ?

 

[dilalio]

which boiler ? S plan or Y plan ?

Worcester (greenstar I think, combi with internal panel clock).
Now using it as system boiler.
S plan.

Now thinking it might be the legionella setting on Nest?

 

[ianmcd]

Now thinking it might be the legionella setting on Nest?

Yes was going to suggest that, I have been caught out with that before, all Worcester condensing boilers are called greenstar, annoying I know, did you wire the two orange wires from the zone valves to the 240v room thermostat connection on the boiler ?

 

[dilalio]

Yes was going to suggest that, I have been caught out with that before, all Worcester condensing boilers are called greenstar, annoying I know, did you wire the two orange wires from the zone valves to the 240v room thermostat connection on the boiler ?

Yup. Both fire wires (oranges) from MCVs wired to LR (rad symbol) on the boiler control box.
Have to be honest, all WBs look same to me... Just looked for the switched live in.

 

[ianmcd]

Yup. Both fire wires (oranges) from MCVs wired to LR (rad symbol) on the boiler control box.
Have to be honest, all WBs look same to me... Just looked for the switched live in.

a few posts, WB dont like using 5 core or close two 3 cores , but dont think this is your problem here, disconnect the ribbon on the inbuilt programmer on the boiler and see if you still have the same problem, could be a back feed from the boiler

 

[dilalio]

a few posts, WB dont like using 5 core or close two 3 cores , but dont think this is your problem here, disconnect the ribbon on the inbuilt programmer on the boiler and see if you still have the same problem, could be a back feed from the boiler

Yeah... Also been thinking about built in prog being issue.
BUT... having taken HW demand from pin 6 out of heat link AND perm live from pin 5 out of heat link, then reinserting perm live to pin 5... After few seconds, 240 reappears on pin 6...this is surely an issue internal to the heat link? I think!

 

[ianmcd]

First rule of everything mate, disconnect all external controls and then re-connect one at a time, once you get the problem again take a step back and see what you have just done, I fit lots of Nest and Hives and have seen a few with connection issues, but never seen a stuck relay that wasnt caused by wiring it wrong and it fusing in the closed position, not saying it doesnt happen, just never seen it out of the box

 

[dilalio]

Question.... Pin 6 can't get 240v from anything external! Even if fed clean voltage from pin 5 (from external non system source) relay from 5 to 6 should not be made unless Nest inner workings makes that switch!

Been drinking and thinking

 

[ianmcd]

Question.... Pin 6 can't get 240v from anything external! Even if fed clean voltage from pin 5 (from external non system source) relay from 5 to 6 should not be made unless Nest inner workings makes that switch!

Been drinking and thinking

so if any pin , external from anything is connected to another pin, could the live back feed ? hence why 2 port valves have end switches ?

 

[dilalio]

so if any pin , external from anything is connected to another pin, could the live back feed ? hence why 2 port valves have end switches ?

I'll have at it again on Monday morning!

 

[fezster]

Is this a nest 3rd gen?

If HW is on (or legionella programme), the thermostat will show a water drop icon. You can also turn off the legionella setting.

Are you testing the 240V is on terminal 6 with a multimeter with the terminal not connected to anything (to rule out anything external making the cable live)?

 

[dilalio]

Are you testing the 240V is on terminal 6 with a multimeter with the terminal not connected to anything (to rule out anything external making the cable live)?

Yes