Odd issue with Nest controlling hot water

[MrGatch]

Hi,

Heating engineer fitted me a new system boiler and a cylinder recently converting from a combi.

System has three zones controlled by Nests including the hot water.

I've just noticed that the hot water doesn't seem to get warm according to the Nest schedule so I investigated and found an odd issue.

The cylinder appears to be successfully calling for heat occasionally - presumably when its temperature gets low, which is why this issue has taken its time to surface.

However, when the Nest hot water calls for heat, I hear the Nest click on, the boiler fire up, however the 2-port valve doesn't open. So the boiler gets in a tiz and shuts off.

The hot water works if I use the Next boost function and then manually switch over the valve, but the odd thing is when the boost ends the Nest successfully closes the valve.

So basically, the Nest will switch off the hot water but won't switch it on - I have to do this manually.

Does anyone recognise this issue?

 

[Riley]

I’d think there’s a wiring fault.

 

[king of pipes]

Shaun is your man on this sure he will be along soon be patient . Kop

 

[ShaunCorbs]

Wired wrong you got any testing gear eg multi meter ?

 

[MrGatch]

I do have a multimeter. Are there any obvious things I can check?

I'm not a plumber, but am a very competent DIYer.

The bit I don't really understand is why it switches the valve off, but not on.

Thanks!

 

[ShaunCorbs]

yes the hot water cylinder port valve find where that goes into

turn hot water off on nest

open the cover of the wiring centre (not the port valve cover)

find the brown wire for said port valve

multi meter on voltage on 240 ac

one pobe on earth the other on the port valve brown wire

now turn hot water on via the nest (normal not boost)

you should have voltage eg 240v if not its wired wrong

 

[MrGatch]

Brilliant. Thanks for the advice!