Y Plan Vs S Plan

[Christian McArdle]

Advantages of S-Plan:

1. More reliable
2. Simpler to understand
3. Simpler to install and debug
4. Works with simple SPST thermostats
5. Provides volt free contacts (required by some boilers)
6. Is extensible to cover more than just 2 zones (i.e. rather than just heating and hot water, you can have independent timing and temperature control of bedrooms, living rooms, conservatories etc.)

Advantages of Y-Plan:

1. Slightly cheaper (needs one expensive valve, rather than too cheaper ones).
2. Slightly less space required.

Irrelevent. Both Y-Plan and S-Plan provide completely independent control of the zones, although Y-Plan is obviously limited to 2 zones.

Christian.

[TheScullster]

Hi all

Does anyone have a link to a comparison of these systems. Struggling to see the advantage of S Plan, although I have seen a number of posters supporting this.

Currently I have S plan, but will have boiler replaced shortly and need to relocate solenoid valve/pump in existing system.

Currently the program is set for 1 hour water heating only before main heating phase only at start of day.

1 hour water heating mid-day. In the evening we have 6 hours heating with 1 hour water heating included.

Would a Y plan system compromise this in any way or am I missing something here?

TIA

Phil

[Roger Mills]

They both do exactly the same job, and both give independent control over CH and HW.

The main disadvantage of Y-Plan is that virtually all the control logic is built into the 3-port valve's actuator - and if you've read this NG for a while you'll have seen miriads of posts about all manner of CH woes, with a large number of them being a problem with the 3-port valve.

As Christian says, S-Plan is much simpler to understand and also provides volt-free contacts - with the valve motor drive and boiler/pump switching being totally isolated from each other. However, if your boiler controls the pump in order to provide pump-overrun, you're more likely to need a by-pass valve on an S-Plan system.

Given a free choice (which I don't have because I inherited a Y-Plan system!) I'd go for S-Plan every time. Yes I could (and still may!) convert it.

[Christian McArdle]

Yes, I should have mentioned the larger likelihood of needing an automatic bypass valve with S-Plan. Then, of course, many Y-Plan systems need them these days, particularly with the increasing use of unvented cylinders which can't be used as a boiler heat pump overrun dump for safety reasons.

Christian.

[Aidan]

Wiring diagrams & stuff here;

I spent a few hours yesterday and a few more converting my heating from Y-plan to S-Plan.

The Honeywell site doesn't list any of the advantages or disadvantages of one of their systems over another. The one that has come to my attention is that the Y-plan 3-port valve is always open to one port. If the power is off, it is open to the HWS indirect. If you have an unvented HWS storage cylinder, you can't use a 3-port valve system. Well, you can, but you have to use a 3-port valve AND a 2-port spring return valve on the HWS port, which is a bit pointless. Better to use the S-plan system.

Secondly, having the HWS port of the 3-port valve open on power-off is not usually a problem because the boiler will be off. If you've got a boiler with a large water capacity or a thermal store, then it will be a problem because you will get gravity circulation over-heating the HWS cylinder when the system is off.

[mike]

"Roger Mills" wrote in news: [e-mail]:

Go for it - I did mine a couple of years ago, never regretted it, if only for the reason I know what's going on.

All you need is enough room - my airing cupboard was tight!, and it's easy

mike

[Guy King]

The message from mike contains these words:

I'll probably have to do it sooner or later so I can run the UHF in the conservatory. If I'm sensible I'll do it at the same time as changing the HW cylinder.

[Roger Mills]

I posted some pictures of what I proposed a while ago, but i don't think anyone commented - so I'll have another go.

This is what it looks like at present.

propose to replace the 3-port valve with 2 x 2-port valves, but I need to take the pipes up higher and back down again in order to get them in - but there will be a vent pipe connected to the highest point. I also propose to install an atomatic by-pass valve and to tee its output into the cylinder return. [The HW and CH returns join under the floor, somewhere.] After modification, it would look something like: anyone see any problems with this arrangement?

[mike]

"Roger Mills" wrote in news: [e-mail]:

It looks a lot like mine, only my valves are stacked vertically.

I haven't used a bypass, as I have no TRV on my hall rad where the thermostat is, also there's a bathroom rad/towel rail.

If that's really bad, perhaps someone would tell me!

With new, rather neater pipework and wiring, and the valves all in a row, it looks quite nice.

I'm a bit concerned about the gate valve on the return pipe - if I read it right, ISTM it's a bit dodgy to be able to close off the whole circulation like that - but I'm an amateur, and may be wrong, the original installation didn't have one, so I didn't fit one.

And if I had it would be a ball valve :-)

mike

[Guy King]

The message from "Roger Mills" contains these words:

No tank-jacket? (insert smiley of choice here)

Other than that - the only minor niggle is there's only one isolator valve for the tank.

[Christian McArdle]

installation

It is traditional to include a gate valve in order to balance the system. Personally, with a modern boiler and a rapid recovery cylinder, not having it gets you some additional hot water priority. On an old cylinder, though, it could take ages to heat up whilst stealing all the flow. My cylinder is rapid recovery, so I didn't put one in.

Christian.

[Roger Mills]

It's bad if your boiler needs pump over-run. With an S-Plan system *both* valves close when both demands are satisfied - and if the boiler needs the pump to keeo running for a bit after it shuts down, the water hasn't got anywhere to go! With a Y-Plan system, there's always at *one* path open.

I have a gate valve on the cylinder return at the moment, which was installed to balance the CH and HW circuits so that when both are running at the same time the HW doesn't hog all the flow. However, since I have independent timing of CH and HW (uising a programmable stat for the CH) I usually contrive not to run them at the same time - so the gate valve is fully open. In the modified scheme it will disappear anyway - and be replaced by a tee where the by-pass flow joins in.

My concerns about my modified arrangement are these:

1. Currently, the cylinder flow pipe only goes up as high as the top entry point on the coil. In the new scheme, it will go higher and come down again. I don't *think* that matters, but would welcome comments.
2. The by-pass return tees into the cylinder return rather than joining at the same point where the CH and HW returns join. Again, I don't *think* that matters because it will be an automatic by-pass which should only open under pump over-run conditions - when *both* zone valves are closed - so there

*shouldn't be any scope for any obscure reverse circulation to take place. FWIW, I'm also planning to fit a Grundfoss Alpha variable flow pump. Again, comments will be welcomed!

[Roger Mills]

Oh yes there is! The cylinder in encased in a factory-fitted foam jacket - that's what the green stuff is, rather than copper corrosion!

Why is that a problem - it's not an unvented cylinder? Are you talking about motorised valves or manual valves? I may well put some full-bore ball valves in strategic places in order to be able to isolate various components, if I can fit them in.

[Guy King]

The message from "Roger Mills" contains these words:

Yes, sorry, I meant no /extra/ tank jacket. The factory fitted stuff is pretty poor. From experience you'll find you lose a lot less heat if you add a "traditional" jacket over the top. Ours was like yours when we moved in, and a tank would stay hot for a day or so if we went away and turned the hot water off. Now, with a second jacket and lagging on the neighbouring pipes it's still noticeably warm after nearly a week.

[mike]

"Christian McArdle" wrote in news:4475698d$0$15870$ [e-mail]:

Thanks for explaining, Christian -as my post indicates I thought it was directly in the return to the tank, after the HW and CH had been tee'd. Struck me as very iffy!

mike

[mike]

"Roger Mills" wrote in news: [e-mail]:

Good point - it doesn't apply to me at present, but if I change the boiler; of course, I think I'd get someone in to do that; too much gas fitting!

See reply to Christian

My flow pipe goes higher, so I have an air bleed at the top. It's only been used when refilling.

FWIW, I'm also planning to

I use an Alpha, but I'm not convinced it was a good move; it seems a bit noisy and vicious, the old pump seemed to work extremely well; top speed for blowing out airlocks, bottom speed nice and quiet and worked well.

YMMV

mike

[TheScullster]

Thanks to all respondents for useful info! One other draw back for me on the S Plan route with pump etc in airing cupboard would be cost! Far more 22mm pipe compared to current S Plan ( this has 1 upstair and 1 downstair valve and almost unavoidable pump over).

Phil