Just changed an old hot water cylinder and immersion heat the immersion heater is a heat merchants immersion it is pre wired so just got cable connecters and connected the 4 wires like for like black to black, brown to brown earth to earth and neutral to neutral but when i switched it on thr immersion did not work i checked for power at connector and i have power and correct polarty any ideas whats the prob

JohnnieK Registered User

Did you check for power at the elements inside the cover?

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danjo Registered User

As Johnnie says you should check for voltage at the terminals inside the cap.

However, for safety, I would not use cable connectors. I would connect the element cable directly into the switch.

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mazthespark Registered User

check is thermal overload tripped by any chance may have to be pushed when you first install them or old wiring method miight be still used last ne i did think they were switching neutrals

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Micky Dolenz Registered User

The old way of doing it was taking brown through stat and neutral to sink. You will have to investigate at switch and rewire there if necessary.

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meercat Registered User

new immersion colours
brown -bath
black -sink
blue -neutral
earth -earth

old immersion colours
brown -neutral
black -bath
blue -sink
earth -earth

you will have to redo connection(preferably at switch)
remember to turn power off when undertaking work

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The wiring to the switch is correct (colours) brown to bath, black to sink ect. When i switch the immersion on regaurdless whether it is on to sink or bath i am getting 230V at both brown (bath) and black (sink) terminals at the same time inside the cap when i presume i should only be getting one or the other? So maybe the actual switch on the wall is faulty because 230V is going to both terminals at the same time, i also got voltage on the inlet side of the thermostat and notting on the outlet. IM VERY CONFUSED (im thinking faulty switch) any help please

Micky Dolenz Registered User

Have you tried turning the stat up and then testing? Does stat have a reset button?

The stat is in a dry pocket and will pull out, return to shop and they should replace it, it's about €8 to replace.


Yes it has a over heat stat with reset but that is ok and i have continuity at over heat stat, but what i was thinking is the switch on the wall faulty because wheather i have selected sink or bath i am getting 230V on both brown (bath), black (sink) terminals at the same time at immersion, surely it must be at one or the other whatever one i selected?

danjo Registered User

Open the switch and check the neutral connection also double check the neutral connections at your cable connector. Make sure you have not trapped the insulation there.
From recollection, with a dual immersion the neutral connection on both elements is a common pillar so if you have no neutral connected to this then a voltage will appear on both phase pillars It will appear as 220v as there is no current drawn and therefore no voltage drop.
As I said in my previous post it would be much better to connect directly to the switch.


When you say negative thats the neutral connection your talking about? Sorry im a plumber not a spark

danjo Registered User

Sorry, I am from the era of positive and negative.
Nowdays they are only used in DC and phase and neutral are the proper terms, so you are correct.
p.s. I am not a sparks either .

gsr dog Registered User

hi gsr dog here switch markings you should see l1 that should be 220 l2 should show 0 in off position switch on should show 220 in l2 ifs that shows 220 you have a missing netureal

johneym Registered User

sorry to hijack thread. I am doing the same. I am replacing an old emersion from a dual coil cylinder with a new emersion to a new single coil cylinder. The wiring is the old version as stated below..
old immersion colours
brown -neutral
black -bath
blue -sink
earth -earth
Now that it will be a single coil,which wire do I omit, if any?


Micky Dolenz Registered User

Since you only have one live, pick one. So either make brown or black live. Just cut off the other cable and don't connect.

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