Zone valve -- 2 or 3 port / mid or divertor?

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Hi,
My CH zone valve actuator gave up the ghost today... Getting a replacement tomorrow...

Whilst removing the dead actuator, I realised that my system has 2 x 2 port valves (1 for CH, 1 for HW) whereas in my last home an otherwise identical system had 1 3-port. Not a problem, just a realisation/observation...!

So my question is, what are the merits of 2 port valves vs 3 port valve ? (other than a 3 port can feed 2 things not just 1 .. I get that bit!)

As well as pure curiousity, there's a practical reason for the question as I'm hoping to zone the CH 3 floors of my home separately, as opposed to 1 zone fits-all (inefficiently). My assumption is that I'm best doing this with 3 x 2port valves (1 per floor) in parallel with a 4th one for the HW cylinder coil. (Wiring to activate valves providing the control)

Ta!

jpdw
 
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2 port valves can have more zones, 3port only 2 zones; ch/dhw
3port advantage: 1 cable, 1 valve, no need for bypass
 
So if I'm splitting my heating into 3 zones, then it would be quite OK & straight forward to have 4 x 2 port valves.

All fed from the flow from the boiler&pump;
3 going 1 to each to a heating zone
1 going to the heat exchange coil in the HW tank

To me this seems simpler than using 3-port, where I presume I'd have a 3-port to direct flow to either HW or CH, then the CH side would split into 3 2 port valves to 'enable'/'disable' each heat zone.

The 4 x 2-port allows HW & CH together whereas 3x2p+1x3p looks like it would be HW OR CH not both at the same time?

Having just had 24hrs without heating thanks to an old valve dying, I like the idea of having all valves the same (ie 4x 2port) - I can have 1 spare replacement actuator that would suit any of them.

Does this make sense or am I missing some important consideration?
 
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am I missing some important consideration?
What is the power output of the boiler? Can it cope when all 4 zones are calling for heat?
It currently does - though not really very well - we ensure the timer is setup so that CH & HW do not overlap). HOWEVER, the zoning will be done when we get a new (slightly bigger) boiler fitted....

So yes, the idea would be the boilder WOULD cope with all 4 Z at once.
 
Hi,
My CH zone valve actuator gave up the ghost today... Getting a replacement tomorrow...

Whilst removing the dead actuator, I realised that my system has 2 x 2 port valves (1 for CH, 1 for HW) whereas in my last home an otherwise identical system had 1 3-port. Not a problem, just a realisation/observation...!

So my question is, what are the merits of 2 port valves vs 3 port valve ? (other than a 3 port can feed 2 things not just 1 .. I get that bit!)

jpdw

All in here;
http://content.honeywell.com/uk/homes/systems.htm

One 3-port is cheaper than two 2-ports, so most domestic systems have a 3-port mid-position (CH and/or HWS) valve. You can also get 3-port diverter (CH OR HWS) valves, usually wired to give HWS priority; I think this is just a different actuator on the same valve.

The two 2-port valve system is S-Plan.
Three 2-ports is S-Plan plus.
I prefer the S-Plan arrangement, it makes more sense.

If you have, or change to, an unvented HWS cylinder, you MUST fit a 2-port (spring-return closed) zone valve to it, even if the existing system has a 3-port valve. The 2-port zone valve comes with the unvented cylinder which should, of course, be fitted by someone who has passed the relevant training course. The valve supplied is usually the Honeywell 2-port.
 

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