Nest thermostat can no longer turn on heating

[busbyuk]

About 4 weeks ago my nest stopped being able to turn on or off the central heating on my glow worm 38cxi.

As the boiler looked otherwise fine I figured it was the nest heatlink itself which has been working fine for 3 years. I managed to organise a replacement heatlink from Google but on replacing it I'm having exactly the same issue with the new nest.

No errors are shown on either the boiler or nest. If I press the manual heatlink button it does click like it's turning on the heating but the boiler doesn't respond. If I want heating I have to manually press the heating button on the boiler itself.

I've done a continuity test from the heatlink to where the wires connect into the Glow Worms PCB board and that is fine. Beyond that though I don't have the expertise or knowledge to know if the PCB itself is faulty. I've checked for cracks/corrosion etc and it looks fine.

Is it a matter of simply replacing the pcb at this point? Seems like an odd thing to just stop working without any other symptoms of issues.

Thanks

 

[ShaunCorbs]

What heating button on the boiler can you post a picture up ?

 

[Aquarius]

How is the nest thermostat wired?

 

[busbyuk]

What heating button on the boiler can you post a picture up ?

Added picture. It's just pressing mode until the radiator picture comes on or the timer/radiator picture and then the heating comes on and stays on.

How is the nest thermostat wired?

It's all going into the controller box which looks like the attached image (not my actual controller but it looks the same)

Live/Neutral/Earth goes into their corresponding points in the controller box

From the nest '2' goes to the '24v' terminal and '3' goes to the '0v' terminal

I didn't wire it in this way as I had a plumber do it but it's worked fine this way for the last 3 years so I think it's correct. When I replaced the heatlink and just turned off the power and wired in the new heatlink using exactly the same method.

Thanks again for the replies.

 

[ShaunCorbs]

When the rad symbol is on does the nest work correctly?

 

[busbyuk]

When the rad symbol is on does the nest work correctly?

Nope. If the rad symbol is on then the heat comes on but the nest/heatlink is unable to control the heating at all. Even if I click the heat link button itself. You hear the heat link click like it's trying to Turn it on or off but nothing happens.

Thanks

 

[Aquarius]

I was asking about the thermostat, not the heat link. That said, if the heatlink isn’t responding (was thinking there isn’t enough charge in the thermostat) then I’d say it’s an issue between heatlink and boiler.

 

[spanner]

What happens when you press the override button - on heat-link does boiler fire up ??

 

[busbyuk]

What happens when you press the override button - on heat-link does boiler fire up ??

Thanks. It does not. I hear the heatlink click but the boiler doesn't respond. Same occurred on the previous heatlink so I'm sure it's the boiler side not working.

 

[spanner]

So if I remember the heat - link is Linked common - Live on on the heat link to 1??
theres a call Puts Live down on 3 which is connected to the R room stat Link on boiler harness??
Might be wrong as the call on most combis the same..
Is wired like this?
THERE IS A NEUTRAL WIRE IN PLACE HERE???????????????
Check ALL the insulated connectors are stripped back enough and you've got them properly in terminal strips