Nest thermostat worcester 12i

[Misha86]

hi
I have a problem with My new thermostat that was installed by a nest pro but failed to run hot water.the person ho installed the thermostat blamed a faulty motorised valve from hot water tub.
I replaced that valve and problem still there,hot water is not coming on even if manually overriding nest transmitter and manually opening the valve,boiler is not turning on.

Reading some of few post here I noticed someone had the same problem and was advised to wire cables like my receiver with the difference that black cable should go in slot 3 and grey cable in 5.
Or anyone with knowledge can you please look at my pictures and tell me please if there is something wrong there.

Cheers

 

[stem]

I noticed someone had the same problem and was advised to wire cables like my receiver with the difference that black cable should go in slot 3 and grey cable in 5.

The colour of the wires is irrelevant and will vary from installation to installation depending upon the personal preferences of the installer. One installer may use black for the 'heating call for heat' another may use grey. It is what is connected to the other end of each wire that is important.

The wire in terminal (3) controls the central heating, so if that is working as it should, it will be correct, If you move it, your heating won't work.

can you please look at my pictures and tell me please if there is something wrong there.

As far as your photos go there are wires in the correct terminals, but whether or not they are connected to where they should be at the other end I can't tell.

The Heat link terminals that control the hot water are (5) and (6)

Terminal (5) of the Heat link should be connected to a live supply and I can see that it is.

Terminal (6) of the Heat link should be connected to the brown wire of the Hot Water motorised valve via the hot water cylinder thermostat, with the connections usually made in a wiring centre.

The Heat link is quite fiddly to wire, so if the hot water was working OK before the Heat link was installed, I would first be checking that the wires in terminals 5 and 6 are secure and that the terminal screw is firmly on the wires and not on the insulation. If that doesn't fix it, you will need someone competent to follow the circuit through with a multimeter from the Heat link to the motorised valve to find out why the circuit has failed.

even if manually overriding nest transmitter and manually opening the valve,boiler is not turning on.

The motorised valve is responsible for starting the boiler, it has an internal switch that operates when the valve is fully open. The manual lever doesn't move it far enough to operate the switch, so I wouldn't expect the boiler to start.

 

[Misha86]

Thank you for reply
Hot water was working ok before, I’m struggling to find someone at this time of the year,apparently this job is to small so are not interested,however one of the heating engineers told me on the phone that my Worcester boiler need a recalibration/calibration for this thermostat.
So I’m not sure what this means and how to do it.
And the person ho installed the thermostat told me that I need a heating engineer.

 

[stem]

That sounds very odd to me.

The Nest Heat link is wired to the motorised valve, it isn't even connected to the boiler! Here's a simplified diagram from page 22 of the Nest manual. I have deleted the other bits that aren't relevant.

Electrically, the Heat link is just a simple on/off switch exactly the same as your previous programmer was, so nothing has changed.

The bottom line, is that the Heat link should open the motorised valve (called water valve above) via the hot water cylinder thermostat (called hot water tank above). You say that the valve isn't opening. If that is correct, there is a fault somewhere between the Heat link and the motorised valve.

It is possible that the valve may be opening, but is not operating the boiler. It's easy to test. With the hot water set 'on' and the cylinder thermostat 'calling for heat' the valve should be open, if it is the manual lever will feel loose and floppy (no resistance) when you move it. If the resistance is there, the valve is not open.