Boiler: Grey wires from valves connected to N instead of L. Does it matter?

Hennymore · 15 December 2017 at 8:43PM

I'm mapping out our heating system in preparation for some changes. I don't know much about these things, but I'm learning.

It's an S plan. I noticed that the grey wires from the water and heating valves share a screw connector with the neutral wire coming from the boiler.

Looking at schematics of what an S plan is supposed to look like, I get the impression that the grey wires should connect to live, not to neutral.

Do I have this right?

Does it matter? What would be the practical consequences of leaving it as-is?

Alex1983 · 15 December 2017 at 8:50PM

If everything is working ok then it will just mean the blue is being used as a live.

Hennymore · 15 December 2017 at 8:57PM

Thank you. Yeah, I had the same thought – the cable is blue, but I have not opened up the boiler's terminal block to verify what it's connected to on that end.

Do I understand you correctly that if the blue is indeed neutral, the heating would not work if connected this way?

Everything is working OK except for intermittent issues with water not heating (asked about it in another thread). My current theory about those issues is that the thermostat wasn't attached well, and glitching. I guess that wiring greys to neutral wouldn't lead to intermittent issues, but to permanent ones?

Hennymore · 15 December 2017 at 9:01PM

I looked again, and the brown wire in the same bunch of wires as the blue goes to the valves' orange wires via a screw connector. That's also supposed to be a live. So if the blue is indeed a live, then there are two lives in that bunch of wires.

Alex1983 · 15 December 2017 at 9:14PM

You lost me abit, the orange is the switch live from the valves, once the valve motors open it makes a switch and sends 240v down the orange to the pump and boiler. The brown in the valve is the motor, that comes from the room stat or cylinder stat and operates the motor and the grey is permanent live, usually from the fuse spur or programmer.

It’s not unusual for people to use blue or earth cables as lives in central heating wiring as there usually to lazy to get a cable with the correct cores.

Hennymore · 15 December 2017 at 9:20PM

What I meant was that there are several thick white cables coming out of the boiler's terminal block. Each such cable consists of a brown, a blue and a yellow/green wire. The same cable that brings its blue wire to the greys also brings its brown wire to the oranges. So I guess that could mean that both the brown and blue in the same cable are live wires. None of them neutral. That just seemed odd to me, but I guess it's par for the course

So just to make sure I understand you correctly: if the blue had been neutral and connected to the greys, the heating would definitely not have worked? No chance?

EDIT: After re-reading your reply and studying the schematics more, I think it's starting to click. I hadn't realised that there's more than one "live" involved - both a permanent live and a switched live. Makes sense now…

Risteard · 16 December 2017 at 6:31PM

Totally unacceptable and the cowboy who did it should be made correct it. Makes you wonder what other nonsense they have done. They shouldn't be playing with electricity.

Alex1983 · 16 December 2017 at 7:00PM

That’s a bit extreme, it’s very common on heating system to see blues used as lives, sometimes sleeved sometimes not. Nearly every time the cylinder stat is wired up with a live, neutral and earth flex and all three will be lives. Not something I do personally but see it daily.

bris · 17 December 2017 at 1:40AM

Blue is always neutral, grey from the valves always permanent live brown and orange on the motors. That's the right way but there are some who get it wrong, and it is wrong even though it works.

S and Y plans are pretty confusing though so for a lot of installers trial and error usually gets there in the end. But it does get confusing for maintenance. Tracing the wires back from the terminal blocks they are connected to can clear it up if you know what goes where.

Alex1983 · 17 December 2017 at 6:04AM

Bris I think your confused what we mean. The op has cables that have blue being used as lives, not the blue from the valve. They have obviously used cables without enough live cores. S plan would not work with the zone valve grey wired to neutral, it would blow the fuse instantly. S and Y plan in my opinion are straight forward system designs but agree I’ve worked with guys that do struggle sometimes, also had to sort out wiring messes from brand new installs where my old company has had electricians do the system wiring.

Boiler: Grey wires from valves connected to N instead of L. Does it matter?

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