Unvented wiring .

EvilDrPorkChop said:

Isn't as simple as that unfortunately. As the HW Stat on a 3 port fires the boiler when it's just HW only. If the heating was running on the 3 port (So Live on the Orange wire on the 3 port) , it would back feed and hold the HW 2 port valve open. Therefore defeating the object of a thermal cut out.

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EvilDrPorkChop said:

As the HW Stat is wired to fire the boiler (HW on to Common on stat, then 1 to S/L on boiler). Then the Orange wire for CH only on the 3 port is wired into the boiler at the same terminal (So your S/L on the boiler). So when you wire your additional 2 port into the 1 terminal on the HW stat (So that the 2 port closes when the stat breaks) if there is still a feed on the S/L to the boiler from the heating side the 2 port valve would still have a live feed and stay open.

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ShaunCorbs said:

no it wouldnt

perm live to stat in

stat out to brown eg port valve open

neutral and earth the same done

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EvilDrPorkChop said:

Yeah, and the stat out also would have to go to boiler S/L. So if your S/L on the boiler is live from another source, so the heating. The valve would still be live and hold open.

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townfanjon said:

Strange request for Easter Sunday lol , its just

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chris watkins said:

Every unvented manufacturer will provide a wiring diagram in their instructions for the use of the 3 port mid position valve & the required 2 port that must be installed with it. This is required as under fault conditions there could be an open pathway from the heat source to the cylinder allowing the cylinder temperature to go above 100deg C.

The only exception to this, to my knowledge, is Vaillant who applied & got a dispensation so long as their boiler & cylinders are used together as a package.
Megaflo one below Jon, whats the cylinder?
View attachment 38257

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