Nest Thermostat uk

[E45y]

Hi, I had a nest 3rd gen thermostat fitted and I have follow the necessary Y plan wiring diagram for my heating system. My issue if that the thermostat has no control over the heating or hot water... I can turn both off (from the stat) and the boiler still burns on... 

Having wires various nest thermostats before I am baffled... I thought it might be the motorised valve but that is operating as it should. 

I have used my multi meter on the heat link across N to 2 & 5 = 240v as it should.

But across N to 3 heating its 240v with the heating off and thermostat down, also with hw off I have 240v across N to 4 and 6.

Any idea why?  Is this a problem with a faulty heat link possibly?

Many thanks

[Vladut]

Hello there, thank you so much for reaching out.

Can you tell us if you've tried to remove the wires in the Heat Link without Live and Neutral and test the voltage between L-N, L-E and N-E?

[E45y]

Thank you for the quick reply, I will check that tomorrow 👍

[Vladut]

Thank you so much. Let us know how it goes. We're one message away!

[E45y]

Ok so I have disconnected the heat link from its power source as you say and have no voltage across terminals 2, 3, 4, 5, 6 as I would expect. I have changed my 3 port valve as I thought this was the issue but upon turning back on I'm faced with the same problem still... boiler constantly on and the thermostat doesn't do anything even with heat and hot water settings off, legionnaires turned off... I don't know what to try next...

[AlexD]

Thanks for trying and letting us know @E45y . 

Just to check, is the system still on with the Heat Link disconnected from power? Or did you connect it back after changing the valve?

Do you have any additional timers or programers in the system? 

Best regards,

AlexD

[E45y]

Thank you for the reply,

No additional timers or programmers on my system.

I'll be honest I didn't check to see if the boiler was still firing after the heat link removed... Nut I was when I wired the new valve in... I'll check when I'm home to see if it continues to run with the heat link removed and let you know. 

I have tried all the rest procedures for both heat link and the thermostat... not sure what else it can be...

Thanks again for any help 😬👍

[E45y]

Ok so an update, with the heat link removed the boiler does not fire... I'm assuming now it's a faulty unit..? Does anyone think it's worth returning for a replacement (only a week old) and trying again or am I missing something glaringly obvious.... 

Any more help is appreciated...

[E45y]

Another update...

I have since removed the cylinder stat cable from the wiring centre. (I'm just trying to get something workig now). So I am just dealing with the heating...

The boiler still runs constantly even with the heating set to off or below the current temperature (bacteria protection is off still). But if I switch it to manual mode on the heat link (all lights on) the boiler stops run... so it appears to be in an off/idle state... 

Any ideas?!?! I running out of patients with this Nest thermostat now...

[AlexD]

Sorry for the late reply.

That behavior is quite unexpected @E45y. When the manual mode is switched on you would expect to turn the whole system on and when it is switched off to turn it off. 

How is the system currently behaving? Do you still have the Heat Link in place? 

[CristianC]

Hello again, 

Just checking in. How's it going with your thermostat?