Navigating my central heating circuits and fitting 3rd Gen Nest

[davemate23]

@ban-all-sheds i agree, but I didn’t wire that. I’m looking for advice on why the circuit is shorting and as I mentioned, once it’s functional i’ll replace the wires.

 

[EFLImpudence]

1 - Live
2 - Neutral
3 - Earth
4 - Blank
5 - CH on (valve white)
6 - HW off (cylinder C)
7 - HW on (valve grey, cylinder 1)
8 - CH on (pump L, boiler L, valve Orange, cylinder 2)

You have HW off and HW on the wrong way round. Is this just written wrongly or connected wrongly?
Plus the Cylinder stat is connected wrongly and you have two CH ONs.

5 - CH on (valve white)
6 - HW on (cylinder C)
7 - HW off (valve grey, cylinder 2)
8 - CH on (pump L, boiler L, valve Orange, cylinder 1)

I haven't looked at your pictures so I don't know what is causing the trip.

 

[davemate23]

@EFLImpudence thanks, and sorry yes - terminal 6 is HW on and 7 is HW off as you have rightly changed.

Is the cylinder stat connected wrongly? According to the Nest wiring diagram C should be on HW on (terminal 6), 1 should be to HW off (terminal 7) and 2 should be to boiler/pump (terminal 8 ).

 

[davemate23]

I just tried switching the cylinder stat 1 & 2 wires (although I actually realised I had them as @EFLImpudence had suggested) - so this was now:

7 - valve grey cylinder 2
8 - valve orange, cylinder 1, pump and boiler L

I said it was this way around before as (maybe I’m being an idiot but) that’s what the Nest wiring diagram (previous post) seems to suggest, but having relooked through the Honeywell diagrams (above) they state as @EFLImpudence does, which is how I had originally wired them.



The power came on after changing the fuse, tried HW on first and nothing happened, then I tried heating and the fuse blew again. I’m assuming the cylinder stat is wired incorrectly this way and therefore the hot water remains off as the boiler didn’t come on (and the circuit didn’t blow on just HW).

It sounded like the valve clicked over when I turned the heating on, so I’m once again assuming that it’s either the boiler or pump that’s shorting the circuit?

 

[AndyPRK]

So you can see I was justified when I said disconnect the nest and motorised valve (CH parts) and get the HW working first, if turning the CH on blows the fuse.

Once you have ruled the boiler/pump in or out as the problem, and have working HW, then try and add in the nest and motorised valve.

No need to refit a timer. Just connect Live to HW on.


P.S There is so much copper wire showing, it wouldn't surprise me if a fray of wire was shorting to a terminal next to it. The nest looks susceptible to this although their layout is unlikely to be your problem

 

[davemate23]

Thanks @AndyPRK . I've just tried what you suggested - nothing happens, but there is a voltage coming through. I'm assuming that without the boiler powered and inline, then there shouldn't be anything happening, am I right?

 

[AndyPRK]

Honeywell and Nest seam to label the hoot water stat terminals 1 and 2 differently! This should explain why the water didn't work.

You mean there is voltage, and no fuse blowing ?

 

[AndyPRK]

Using the correct wiring center terminal numbers wire it up as follows.

A loop of wire from the live terminal to HW on. Term.6 ? (this is to act as a HW timer)
The HW stat COM wire to pin 6
The HW stat CALL (1 honeywell) for heat to pin 8
The HW stat SATIS (2 honeywell) to pin 7
The boiler L to pin 8

It's very important to get the HW stat wires correct.

If you have a contunity tester (with power off) the COM and CALL wires should be connected and buzz

or dare I say it, if you have a neon screwdriver, check the stat COM wire is live.
and then the CALL wire should be live to turn boiler on.
If the other STATIS wire is live (and you don't have a recently heated tank) then that is a problem and the 2 wires need swapping

It's also worth removing the HW stat cover if you can, and ensure the COM wire is identified correctly. It will only screw you later on, if it isn't

 

[ban-all-sheds]

@ban-all-sheds i agree, but I didn’t wire that.

Never thought you did - it woz a plummer wot dun it.

 

[ban-all-sheds]

Honeywell and Nest seam to label the hoot water stat terminals 1 and 2 differently!

They're 'avin a laugh.

 

[davemate23]

Thanks @AndyPRK - Yes, I meant voltage and hence no fuse blown. I've already removed the stat cover and checked. It's a Honeywell stat, so I have been using Honeywell's diagrams.

There's still voltage to the system with the Nest and Valve reconnected, so just the pump and boiler attached. I'm thinking about just connecting the pump the live now to test it alone - I'm assuming this will just pump the system around the radiators, but also assume I should connect the orange wire to the live as well to ensure the valve is open correctly?

 

[AndyPRK]

well that's a rather silly way to fault find, connecting the nest back up.

There must of been a reason why the hot water didn't work before. Either the nest not enabling it or the stat wires wrong.

Yeah power the pump up if you wish to gain confidence its ok. Should pump water around the tank with valve not powrered

 

[davemate23]

So you can see I was justified when I said disconnect the nest and motorised valve (CH parts) and get the HW working first, if turning the CH on blows the fuse.

Once you have ruled the boiler/pump in or out as the problem, and have working HW, then try and add in the nest and motorised valve.

I thought you had suggested it? Ah well. Pump works fine on it's own, I'll try wiring the boiler in-line with it and the orange valve and see what happens. I'm assuming this will blow it as the boiler is the only component left!

There is a live connection through the cylinder stat, so it seems like it's wired correctly.

 

[AndyPRK]

I was just hoping you would get working HW first.

 

[davemate23]

Doesn't the HW have to come from the boiler?

Connected the boiler to the pump and orange wire of the valve and the fuse blew again. I've now reconnected everything except the boiler and it seems to be clicking as you would expect and maintaining a live connection... so I guess it's got to be an issue with the boiler... maybe the PCB or something.