2 port wiring question

[jonnyswamp]

Haven't been on for quite a while, but have a question for greater minds than mine
Have an unvented to change which is currently controlled by a 3 port, will be fitting a 2 port to the flow when cylinder is changed
Apart from changing to S plan (which isn't really an option) how do I wire the 2 port into the existing 10 way and hi limit stat
Gracias in advance
BTW I am G3, don't know why I can't access that part of the forum, did send my details previously

 

[ShaunCorbs]

In short just wire it to the cylinder stat

Live to the cylinder stat
Port valve brown on the outlet / call side

 

[jonnyswamp]

In short just wire it to the cylinder stat

Live to the cylinder stat
Port valve brown on the outlet / call side

Keeping the existing 3 port wiring?

 

[ShaunCorbs]

Keeping the existing 3 port wiring?

yep its only there to stop overheating

 

[EvilDrPorkChop]

Can't do that. If you put the Brown wire to the call side of the Cylinder Stat, as the cylinder stat is used to fire the boiler directly on a 3 port whenever there is a demand at the S/L for the boiler the 2 port MV will open regardless of whether the cylinder stat is open or closed. Completely defeating the object.

 

[ShaunCorbs]

Can't do that. If you put the Brown wire to the call side of the Cylinder Stat, as the cylinder stat is used to fire the boiler directly on a 3 port whenever there is a demand at the S/L for the boiler the 2 MV will open regardless of whether the cylinder stat is open or closed.

cylinder stat wouldnt be used to fire the boiler with a 3 port as you wouldn't have a a sat port

 

[EvilDrPorkChop]

cylinder stat wouldnt be used to fire the boiler with a 3 port as you wouldn't have a a sat port

Thats my point, it goes straight to the boiler S/L. So when the Orange wire becomes Live on the 3 port the Cylinder stat wire becomes live. Usually this wouldn't matter as your cylinder stat would be open or closed, but as you've wired the 2 port in after this contact it'll back feed and open the 2 port valve whenever there's 240v on your orange wire from the 3 port.

 

[ShaunCorbs]

Thats my point, it goes straight to the boiler S/L. So when the Orange wire becomes Live on the 3 port the Cylinder stat wire becomes live. Usually this wouldn't matter as your cylinder stat would be open or closed, but as you've wired the 2 port in after this contact it'll back feed and open the 2 port valve whenever there's 240v on your orange wire from the 3 port.

how as the stat would get wired into perm live

i dont get what your saying

perm live to unv stat
brown of two port to call of stat

and rewire the 3 port to get rid of the old gravity stat and use it on the timer

so how would the port valve get backfed

 

[EvilDrPorkChop]

how as the stat would get wired into perm live

i dont get what your saying

perm live to unv stat
brown of two port to call of stat

and rewire the 3 port to get rid of the old gravity stat and use it on the timer

I don't get what you're saying either?

So you've now got no temperature control with your clock, other than the 2 port MV shuts when the cylinder reaches temperature. So when the customer leaves the timer on 24/7, what's shutting the boiler down when the cylinder reaches temperature? As from what you've said the 2 Port MV is just wired into the cylinder stat that has a Perm live and isn't doing any boiler control with it's microswitch.

 

[ShaunCorbs]

I don't get what you're saying either?

So you've now got no temperature control with your clock, other than the 2 port MV shuts when the cylinder reaches temperature. So when the customer leaves the timer on 24/7, what's shutting the boiler down when the cylinder reaches temperature? As from what you've said the 2 Port MV is just wired into the cylinder stat that has a Perm live and isn't doing any boiler control with it's microswitch.

correct as most dont have any sat ports on your unvented cylinder stat so you cant control them like that

thats why they always recommend to upgrade to an s plan

you could install a 28mm port valve and use the white wire as satisfied eg powered when closed

 

[EvilDrPorkChop]

correct as most dont have any sat ports on your unvented cylinder stat so you cant control them like that

thats why they always recommend to upgrade to an s plan

you could install a 28mm port valve and use the white wire as satisfied eg powered when closed

Every unvented cylinder stat I’ve come across has a satisfied port. Even on the Megaflo/OSO inbuilt stats do.

The way your suggesting to me wouldn’t meet any energy efficiency regs at all. As the boiler could be firing with no demand needed from the cylinder.

I do agree though trying to use a 3 port with a 2 port is daft. It’s better to convert to a S plan system.

 

[ShaunCorbs]

Every unvented cylinder stat I’ve come across has a satisfied port. Even on the Megaflo/OSO inbuilt stats do.

The way your suggesting to me wouldn’t meet any energy efficiency regs at all. As the boiler could be firing with no demand needed from the cylinder.

I do agree though trying to use a 3 port with a 2 port is daft. It’s better to convert to a S plan system.

last mega flow and gledhill 300-400l didnt the stats had no ports (as any stat does) but not wired up

havent fitted an oso so cant comment

 

[wattsie1987]

Normally open 2 port powered closed from cylinder stat sat or hw off on prog?

 

[EvilDrPorkChop]

Here's the diagram you need.