Nest Wiring issues 3rd Generation

CBW said:
Sorry, I’m lost with this. The heating isn’t coming on if the wire is removed (I understand that), he can control the hot water from Nest (i understand that), issue with the Nest (I don’t understand that).
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Unless I've missed something, as I understand it:

The problem the OP has is that whenever he turns the power on the heating comes on regardless of the Nest heating control settings. ie if the heating is required or not, it comes on, and the CH On from terminal 3 of the Heat link remains permanently live, even if he manually turns the heating off at the Heat link button.

As far as I can tell the hot water is working as it should when the heating is running, which in this case because of the fault is permanently.

Removing the wire from HL 3 simply removes the live from the MV white wire which stops the heating coming on, as would the HL if it actually turned terminal 3 off.

Not sure I explained that very well :confused:
 
@CBW
Im not an expert at all but the those two wires crimped together came from the old programer (British Gas, nest looking system, but not nest) and the British Gas labelled Drayton thermostat. They then went together into ten. I took the cable used for the old thermostat and used the brown and black wire for T1 and T2 connections on the heat link. I have then wired from the heat link into 10 as HW on from terminal 6.
Hope that makes sense.
I was wondering if its an issue with the two wires you mentioned but I don't know how they would affect the heatlink unless on of course was hot water off or Heat Satisfied??
My knowledge doesn't extend to answering that question
 
Sorry, I’m still learning electrics side of my job too, so it seems that the heat link is faulty?
 
Yes, terminal 3 of the Heat link should only be live when the Nest switches the central heating on. It moves the motorised valve to the heating position via its white wire.

In this case terminal 3 is permanently live, so the valve remains in the heating position and is permanently 'on'. Removing the wire from 3 simulates the Heat link switching terminal 3 'off' and the heating goes 'off'.

Unusual fault, I've not come across it on a Heat link before. I have found it on other programmers where a short circuit has occurred and has welded the heating contact together inside the programmer so the heating is permanently 'on' but the OP says that hasn't happened.
 
The problem is we don't know if line. This upload_2021-10-25_15-22-59.png shows there is a potential difference between his thumb and the terminal, but we don't know if the relay is open or closed.

If we look at the wiring of a mid position motorised valve mid-position-valve.jpg we see there are numerous paths current can take, and only showing one make of motorised valve. Using a meter and reference to neutral we can seen if volt drop across resistor or diode and we have a chance. But a neon screwdriver is a great tool to identify when we have borrowed neutrals, or any other reason why power returns while working on some thing, but useless as a test meter.

I remember working on daughters Y plan, and I was really scratching my head, at that point I did not have internal plan of the valve, and it turned out one of those micro switches had stuck, also had problems with Nest Gen 3 with boiler firing up when no heat called for, which was simply the anti legionnaires software kicking in.

So you have 3, 4, and 6 output from heat link, 3 connects to white on motorised valve, 4 connects to grey hot water off, and 6 to orange boiler run. Colours are wires of the motorised valve, no other colours can be trusted as correct.

So Grey does nothing unless white is powered, if white is powered then it makes the valve go all the way over so no DHW, and Orange is an output. For DHW only the motorised valve is at rest, and the orange is made line direct from the tank thermostat.

White (3 on heat link) is connected with a resistor and diode to orange (6 on heat link) so if the boiler is running due to DHW being on, the white will still likely have enough power to light a neon, however it is likely less than mains voltage how much less depends on the ohms per volt of the meter being used.

So remove the wire in 3 of heat link and put in a connector block to keep safe, and then test output of heat link. Even a table lamps with tungsten bulb is better than a neon screwdriver, the neon screwdriver uses so little power.
 
The Nest Bacterial Prevention function switches on the hot water, not the central heating. An Icon on the thermostat display shows when it's operating.

I agree about the mains tester screwdriver being a poor tool. A multimeter would be my weapon of choice. However as the motorised valve synchronous motor requires AC mains voltage to operate and wind it across to the heating position I think we can be fairly confident that's what is present on terminal 3.
 
Reply to Google for their requested information
>>>proof of having 230V in Neutral
>>tests that need to be done:
Live-Neutral 230V Confirmed
Live-Earth 0V Confirmed
Neutral-Earth 0V Confirmed
>>> wiring is done correct for 2-3? if so where is 2 wire coming from? as well is the 3 wire connected to switch live on the boiler
The wiring for comes from the L
we need continuity test if the activation is problematic

with no wires in the HL, except Live and Neutral, assuming they come from the right source and in the correct order, and t1-t2:

Set thermostat to 9 degrees, make sure is not calling for heat
Continuity between 1-2 positive or not? Open Circuit
Continuity between 2-3 positive or not? Closed Circuit
Set the thermostat to call for heat, preferable ax temperature to be sure
Continuity between 1-2 positive or not? Open Circuit
Continuity between 2-3 positive or not? Closed Circuit
For Hot Water with no Boost
Continuity between 4-5 positive or not? Closed Circuit
Continuity between 5-6 positive or not? Open Circuit
For Hot Water with Boost
Continuity between 4-5 positive or not? Open Circuit
Continuity between 5-6 positive or not? Closed Circuit

This confirms to my simple knowledge that the circuit for the heating remains open and doesn't close regardless of what temp
 
Having had a new heat link sent over the system still isn't working. The circuit open and closes now as it should be the heat is permanently on? Can anyone suggest what's wrong with the wiring on this system please.
 
So, you told us originally that if you removed the wire from Heat link terminal 3 (which was permanently live) the heating didn't come on. When you put it back in the terminal it did come on.

Are you now saying that if you remove the wire from terminal 3 of the new Heat link, the heating is on?
 
Check the settings on a nest. When you first set it up it has disinfection enabled which means it wants to to do 1 hour of hot water first. I always disable this.
 
snb said:
Check the settings on a nest. When you first set it up it has disinfection enabled which means it wants to to do 1 hour of hot water first.
Click to expand...

We've been down that route already....
stem said:
The Nest Bacterial Prevention function switches on the hot water, not the central heating. An Icon on the thermostat display shows when it's operating.
Click to expand...

The problem the OP has, is with the Heating staying on, not the Hot Water.
 
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