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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Electrical Questions >> stat wiring for new unvented cylinder https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1345739549 Message started by morty on Aug 23^rd, 2012, 5:32pm

Title: stat wiring for new unvented cylinder
Post by morty on Aug 23^rd, 2012, 5:32pm

Hi all,
Just a quick question,had vented indirect system in house and changed to unvented indirect as we will be building into loft & wanted rid off the massive water tank.
My question is that on the new tank there is a thermal cut -out wired into a thermostat,no problems there but have noticed that there are now 3 connections,terminal 1 to 1 on cut out & 2 on cut out to 1 on thermostat with 2 & 3 on stat going to 2 & 3 on terminal block.I presume 3 would be used if I didn't have an "S" plan system & would go to the 2 port valve supplied with the tank if I had a "Y" plan.where as before it was just a 2 wire stat on old tank or am I talking nonsense,can't see anything in manual.Your thoughts are appreciated.

Title: Re: stat wiring for new unvented cylinder
Post by Lectrician on Aug 23^rd, 2012, 6:51pm

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.

Title: Re: stat wiring for new unvented cylinder
Post by morty on Aug 23^rd, 2012, 8:51pm

Hi lectrician,
thanks for reply,I've put the fluke across contacts 1 & 2 on terminal rail,ie power in through 1 to thermal cut out & out through to terminal 2 via stat & its closed circuit which I would expect it to be until temp is met & stat opens circuit switching of signal to boiler.
Trying to upload jpeg but having probs.

Title: Re: stat wiring for new unvented cylinder
Post by thescruff on Aug 24^th, 2012, 12:44am

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.

Title: Re: stat wiring for new unvented cylinder
Post by morty on Aug 24^th, 2012, 3:17am

Hi for some reason the wiring page was missing from the manual for 2x 2 port valve system.Have now found manufacturer of cylinder as WW put their own stickers on it.Its a centrestore 210lt.
PDF found at

http://www.plumbcenter.co.uk/wcsstore7.00.00.446/ExtendedSitesCatalogAssetStore/images/products/AssetPush/DTP_AssetPushHighRes/std.lang.all/ti/on/Center_Centerstore_Installation.pdf

Your help is appreciated.

[edit]Images added by Lectrician[/edit]

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Title: Re: stat wiring for new unvented cylinder
Post by Lectrician on Aug 24^th, 2012, 6:54am

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?

Title: Re: stat wiring for new unvented cylinder
Post by morty on Aug 24^th, 2012, 7:27am

Cheers for that lectrician,yep I had noticed that 2port would have to be wired in series with cut out & stat if I had "Y" plan instead of "S" plan.Could I get that drawing uploaded no I couldn't, I tried everything.
Much appreciated.

Title: Re: stat wiring for new unvented cylinder
Post by morty on Aug 26^th, 2012, 10:40am

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.

Title: Re: stat wiring for new unvented cylinder
Post by Lectrician on Aug 26^th, 2012, 12:17pm

Can you post some pics of the setup?

Email them to me at admin@askthetrades.co.uk if easier for you, and I will post them.

Photos of the cylinder and pipework and wiring if possible.

Does the water/pump sound laboured when it's running on just HW compared to just CH? Blockage perhaps?

Title: Re: stat wiring for new unvented cylinder
Post by morty on Aug 26^th, 2012, 12:49pm

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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Title: Re: stat wiring for new unvented cylinder
Post by Lectrician on Aug 26^th, 2012, 9:13pm

I would say it could be an airlock, but that's more a question Scruff can answer.