Thought power was isolated to boiler & pump

Kealyboy

see picture. I was changing my boiler and central heating pump so I switched off spur on wall in kitchen. When out to garage boiler was off and pump. Slackened off screws connecting LNE. Disconnected bottom two wires in pic (white wires) and lights in garage went off 😕 . Put the wires back in for boiler and pump lights came back on, took the bottom two wire out again and lights went off but the when I just tightened up screws lights came back on. Very confused 😕 is this some sort of loop circuit but when I turned switch off it killed power to boiler and pump. Can anyone explain?

There is two neutrals coming in from the supply, must be something got to do with that maybe…

IMG_4525.jpeg

10-10-20

Ill be nice in advance of later commenters who might not be so nice.

https://www.tradeskills4u.co.uk/blog/safe-isolation-procedures

Keep safe.

Kealyboy

https://www.boards.ie/discussion/comment/123947605#Comment_123947605

thank you for that. Can you explain why this happened? My martindale voltage tester didn’t read anything. Thanks

10-10-20

I guess that power to the temperature controllers and/or zone valves is coming off a different circuit to the boiler.

Make sure to fill out the near-miss forms. 🤟

Kealyboy

https://www.boards.ie/discussion/comment/123947619#Comment_123947619

not trying to be smart but the heating system is not zoned and the power to the boiler (one of the wires I disconnected) runs through a dual boiler stat/ high limit stat mounted on boiler and then runs to the burner.
so I’m still none the wiser 😬

Lenar3556

https://www.boards.ie/discussion/comment/123947642#Comment_123947642

It’s possibly a shared neutral situation. The neutral from the lighting circuit (which is on its own MCB) is being fed back to the board on the same cable as the boiler.
Not ideal.

standardg60

https://www.boards.ie/discussion/comment/123947827#Comment_123947827

Think that's exactly it, hence the two neutrals on the supply side. One of them is the light neutral getting a piggy back back to the board.

Kildaremagnet

This indicates that the boiler circuit is not RCD protected as required. This is potentially a very dangerous situation and should be checked by a professional. Get a Registered Electrical Contractor to check the wiring.

Lenar3556

It is required now, but likely wasn’t at the time of installation.

Given the shared neutral, combining the lighting and heating circuits into a single RCBO would be an improvement.

whizbang

House thermostat fitted ?