Three terminals would be used for Y plan, two terminals for S plan.

It would depend on the make/model of the cylinder as to which terminals are which.

Hold your horses, have You got a G3 ticket to work on unvented cylinders.

The wiring for an unvented is very clear how it should go, including the 2port valve which must be fitted.

Post the make and model of the cylinder and some system details and I'll go from there.

Live from time control to terminal 1.  Terminal 2 then opens the 2 port zone valve (brown).  So assuming you are using S plan, terminals 1 and 2 are of interest to you.

As scruff says, you MUST use an S plan system.   If you used a Y plan, you would HAVE to add the supplied 2 port valve too.  This is a safety requirement to close off the heat source to the tank should the overheat stat operate.  A mid-position valve is unable to move to the HW closed position under all conditions.

The wiring gets a tad more confusing if you are using a Y plan system with the additional 2 port valve too, but I don't think we need to explain that at the moment, as you have an S plan?

Wired stat as per drawing supplied & as I thought it was originally but I think the plumbers have faffed up.Boiler is going out on over temp before stat is getting satisfied above a setting of 2.5.
If I set stat to 3 or 4 the boiler always goes out on over temp before stat operates.Once boiler goes out on over temp if I turn the stat back you can clearly hear the stat break its contacts at around 2.5 and drop voltage to the valve.mmmm just when you think things are going well.

Hi lectrician,
will get some pics just now,I've wired the immersion now to see if the water comes to temp,if it does my intention is to turn the pot on the stat relay up fully and turn it down to see when it breaks its contacts.
looking at the wiring the immersion must use the same inner stat as wiring comes from collar of element to the back of the relay with pot on it.As for the hot water plumbing all they had to do was cut and run 2ft of pipe as feed and return were on different sides from old tank.I did think that they could have blocked something,surely not with 2ft of pipe?.Pump is not labouring but boiler over heats really quickly & pipes at feed and return are hot.To cap it all the flipping hot & cold are reversed on shower,how do these folk get employment????
Since then I've removed the motor from the 2 port valve and the stem and mech are free moving,when limit switch fires the boiler you can clearly feel the hot water flowing on the other side of the valve & the incomer to the tank gets damn hot.Immersion been on a while and when I operated the 2 port the pipe was red hot but return no where near as hot,yep you would expect that thats how it works but not when the water is already roasting from immersion,could this be an air lock???

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