Indirect water cylinder

[fixitflav]

But it is the best method.

That might be your opinion. Re-reading, it looks like the kit isn't installed yet, so it's not a question of changing existing. IMO best plan is to take back the mid-position valve and swap in for a W-plan V4044. If he can then clarify with Viessmann how to connect the roomstat he's pretty much there.
Wiring is simpler also and no limit switches to cause problems.
Even if he decides against weathercomp I would still go for W-plan as IMO Y-plan is no improvement.

 

[dilalio]

That might be your opinion. Re-reading, it looks like the kit isn't installed yet, so it's not a question of changing existing. IMO best plan is to take back the mid-position valve and swap in for a W-plan V4044. If he can then clarify with Viessmann how to connect the roomstat he's pretty much there.
Wiring is simpler also and no limit switches to cause problems.
Even if he decides against weathercomp I would still go for W-plan as IMO Y-plan is no improvement.

Personally I prefer an ntc for cylinder DHW control and no 2 port but just a reversed diverter for primary direction.

 

[desktop987456]

it looks like the kit isn't installed yet

No its not and hence the post. The boiler is working in CH mode only (with your help off course).
I have bought the cylinder, will hire someone to do the pipework. I have attached a photo of pipeloop with mid position valve which I intend to utilize with cylinder installation.
The mid position valve is drayton (see attached picture)
I just want to make an informed decision of which configuration to go for and will buy parts based on the configuration. What's your advise on W plan system? I have to make a decision whether to go for 2 x 2 port valves for X plan or mid pos or diverter valve for W plan?
The WC sensor I will install myself for CH (not sure if I need room stat with WC but that's another debate).

Thanks in advance.

 

[desktop987456]

swap in for a W-plan V4044

So mid Position valve that I have is for Y plan system and have a different actuator.
Am I right in thinking (as you have said in your post as well) that valve body for mid position and diverter valve is the same? Its just the actuator that needs to change from ZA5 (5 wires) to ZA3 (3 wire) system.

I sent out an email to Viessmann Technical support asking them about the cylinder demand terminal box used in conjunction with WC for CH. I have purchase the WC sensor for CH only. They suggested a W plan system as well. I am on my learning curve about various configurations before I make an informed decision with the help of this forum.

Do I need to run a separate circulator/pump for DHW in W plan configuration?
I am also tossing up the idea that whatever configuration I chose it shouldn't disrupt my CH loop which is working perfectly.

 

[desktop987456]

A X plan"
https://heatingacademynorthampton.co.uk/pdhw-pt-3/#:~:text=X plan work?-,A X plan,-is a NO

Thank you for sharing this. A very good read for understanding various systems.

 

[dilalio]

Thank you for sharing this. A very good read for understanding various systems.

The chap who wrote that and runs the courses (which are very good) Kim Betty, is/used to be on here as ecowarrior.

You could go on his course!

Courses - Heating Academy

See upcoming courses here.

heatingacademynorthampton.co.uk

 

[Madrab]

You could go on his course!

Might be a bit of a trek for him from across the pond

I just want to make an informed decision of which configuration to go for and will buy parts based on the configuration

OK - either a W plan or an X plan will work and do the job - the W plan with the diverter is a little easier to plumb in though for a pro an X plan is just as easy. The trick after that is the wiring and config. You need someone who is familiar with boiler wiring and setting up PDHW with OT and the correct controls/stats.

The diverter vavle is a simple on and off - off it's @ HW by default, on it's CH but X plan is the new prescribed standard for PDHW

IMO best plan is to take back the mid-position valve and swap in for a W-plan V4044.

The MID pos valve was a hangover from the last job and an old used valve so can't be taken back

I have bought a 120 litre indirect water cylinder.

Vented or unvented?

 

[fixitflav]

I think if you common the grey&white then the MPV becomes a diverter valve.
This may be of some help.

Priority Domestic Hot Water using a 3-port mid-position valve. - ellse.org

ellse.org

Thanks for that, gives a useful cross-check on Viessmann data sheet. Also shows where the roomstat goes - between CH common on the timer and 8 on the terminal strip.

 

[fixitflav]

The boiler is working in CH mode only (with your help off course).

Remember it now, memory's not what it was!

The mid position valve is drayton (see attached picture)

I'm pretty sure the operation and wire colours are the same as Honeywell, unless somebody corrects me.

I just want to make an informed decision of which configuration to go for and will buy parts based on the configuration. What's your advise on W plan system? I have to make a decision whether to go for 2 x 2 port valves for X plan or mid pos or diverter valve for W plan?

As you already have the valve, may as well use it. Although it's a mid-position type the mid-position is not used with weather comp and PDHW, and it's wired accordingly a la Viessmann. If you feel like getting a replacement either/or valve head that would be wired as W-plan.

So mid Position valve that I have is for Y plan system and have a different actuator.

Different from what? It's a mid-position actuator I assume.

Am I right in thinking (as you have said in your post as well) that valve body for mid position and diverter valve is the same? Its just the actuator that needs to change from ZA5 (5 wires) to ZA3 (3 wire) system.

Yes, valve body is the same.

I sent out an email to Viessmann Technical support asking them about the cylinder demand terminal box used in conjunction with WC for CH. I have purchase the WC sensor for CH only. They suggested a W plan system as well. I am on my learning curve about various configurations before I make an informed decision with the help of this forum.

Starting from scratch W-plan would be a good option, but as you already have the valve.............

Do I need to run a separate circulator/pump for DHW in W plan configuration?

No

I am also tossing up the idea that whatever configuration I chose it shouldn't disrupt my CH loop which is working perfectly.

Only affect on the CH is that when HW is called the CH goes off until the cylinder stat is satisfied (or switched off on the timer)

One more point - the Viessmann data shows a timer with all 6 terminals accessible. Some timers have the both commons connected internally at mains voltage, and inaccessible.

 

[dilalio]

Might be a bit of a trek for him from across the pond

 

[desktop987456]

from across the pond

exactly! Even if it was, I couldn't afford it.

Starting from scratch W-plan would be a good option, but as you already have the valve.............

and as John says, I can use it as a 3 wire system so my inclination is towards a W plan system.

Vented or unvented

Not sure on this one yet. See attached spec sheet which I have short listed.

 

[desktop987456]

The trick after that is the wiring and config. You need someone who is familiar with boiler wiring and setting up PDHW with OT

My boiler doesn't support OT as far as I know so X plan is not for me?

 

[fixitflav]

The MID pos valve was a hangover from the last job and an old used valve so can't be taken back

OK, I'd missed that

Try and avoid using a 3 port mid pos valve (Y Plan), they are notoriously unpredictable and no longer used on new installs - use at least 2x2 port valves (S plan).

I hadn't heard that but I'm not surprised, I never saw any advantage of Y-plan over W-plan

 

[fixitflav]

and as John says, I can use it as a 3 wire system so my inclination is towards a W plan system.

Fine if you're happy to buy a W-plan valve, or preferably just the head, as cheaper and no need to disturb the pipework.

 

[desktop987456]

Fine if you're happy to buy a W-plan valve, or preferably just the head, as cheaper and no need to disturb the pipework.

I will keep the thread alive!