S Plan Zone Valve Grey Wire To Brown Wire?

[FGoogle]

I have just converted my Y plan to S Plan. All seems to work

However the water circuit has never been 'right'

There is an unvented OSO Cylinder in an airing cupboard (in a bathroom) the other side of the house to the boiler.

It has a zone valve controlled by a different circuit to the boiler / time switches etc. There is no call back to the boiler.

So the time switch comes on for the hot water and pumps to that zone. The zone valve cuts in and out (on a different circuit) and the bypass valve deals with the fact that there is no call back from the valve to the boiler.

SO

I thought I would run a wire from the time switch to the unvented tank.

Looking at the standard s-plan wiring for the zone valves the Grey wire appears to be permanent live and the Brown wire is live when the timer calls for the zone to switch on.

Two questions

1. Why does it need the permanent live through the grey wire? Can I join the grey to the Brown? (I can send four wires to the otherside of the house that way)

1. Do I need to get this 'certified' because of part 'P' ?

Thanks

Mark

[Ed Sirett]

Assuming this is an industry standard type zone valve then ou should have an orange wire. This is joined to the grey when the valve is open.

The orange/grey pair can be used to switch on the boiler of course. They can also be used with 'volt free' switching.

HTH

[Roger Mills]

I don't know about any peculiarities of your particular system, but standard S-Plan works like this:

Each zone valve has two independent circuits - one to drive the motor to open the valve, and one (volt-free contacts) to switch other things on once the valve has opened. The motor circuit is driven by the programmer and room or cylinder stat. The volt-free contacts of all valves are connected in parallel - with a permanent live as the input and with the output connected to the boiler and pump. That way the boiler and pump run whenever or or more zones are calling for heat - but only the zone(s) whose valves are open get any heat.

If you cross-connect the motor circuit to the volt-free contacts then *all* valves will open in unison regardless of whether there's a demand in their particular zone. This is *not* what you want!

AIUI, changes to CH control wiring *are* covered by Part P. But who's to know when you did it or, indeed, whether it was originally installed as S-Plan?

[Christian McArdle]

This is one of the reasons why unvented cylinders must be installed by a trained competent person.

The zone valve you are looking at is the safety override valve that was supplied with the cylinder. You must not interfere with it in any way. It should be lashed up to its own dedicated overheat stat. It is the equivalent of an immersion heater's overheat stat.

What you need to do is add an additional functional zone valve to your S-Plan-Plus system. This should be run from your programmer, through a separate thermostat and with the boiler interlock connections used. The unvented cylinder is, thus, separated from the boiler by TWO independent zone valves.

DO NOT disable or interfere with the existing zone valve. It is an important safety device and MUST NOT be used for functional zoning.

Christian.

[FGoogle]

I was looking at the wiring diagram from the manual of the cylinder which shows the wiring diagram for an S-Plan using the valve from as a normal zone valve.

I would have thought that using it in this way would be safer than it currently is (I.e. if the power failed to the current zone valve the boiler would continue to heat it up - if it is on the same circuit as the boiler then it the zone failed - the boiler would also fail)

I agree an extra zone would do the same thing - but then you have 2 x zone valves - is this really necessary? You also say 'through a separate thermostat' - but there is no mention of this method in the manual?

Is it 'normal' to have 2 zone valves on an S-Plan with an unvented cylinder?

Thanks for any help

[FGoogle]

Sorry to sound dim - but I am still confused.

Forget about thermostats for now - lets assume there are 2 x heating circuits

These valves are N/C so no power = Closed

Zone 1 - Live -> Brown and Grey Wires - When the valve opens Live goes onto the Orange Wire

Zone 2 - Same wiring - but is off

Zone 1 puts live on the Orange wire - but as Zone 2 is off (Closed) it doesn't get to the Grey Wire (and hence doesn't get to the brown wire)

What am I missing?

Sorry to be dim

Thanks for the help

[Christian McArdle]

Yes. It is a legal requirement. It is against the law not to have it. The thermostat has to be non-self reseting (i.e. requires a "reset" button to turn back on).

Building Regulations Part G3

3.3 To meet the requirement a directly heating unit or package should have a minimum of two temperature activated safety devices operating in sequence:

a. a non-self resetting thermal cut-out to BS3955:1986 Specification for electrical controls for household and similar general purposes, or to BS4201:1979 (1984) Specification for thermostats for gas burning appliances; and

b. (snipped description of temperature/pressure relief valves).

3.6 Safety devices listed in paragraph 3.3 (see also 3.4) for direct heating are also required for indirectly heated units and packages but the non-self-resetting thermal cut-out should be wired up to a motorised valve or some other suitable device to shut off the flow to the primary heater, that is:

(snip list of approval methods).

Christian.

[FGoogle]

Now I am well confused.

I was trying to put it right as per the manual.

Surely those regs mean the two stats on all unvented tanks (I.e hi stat and control stat)

I looked up 5 different wiring diagrams for unvented cylinders none of them have 2 valves - all have one from the time switch - all of them have a built in thermostat (and a high limit stat) .

Any web references to wiring diagrams with two valves?

[Alistair Riddell]

My S-plan system with system boiler and unvented DHW tank has only one zone valve on the DHW primary circuit but surely the safety cutouts built in to the boiler itself are sufficient as backup safety devices i.e. two zone valves are not required.

In addition to the zone valve and associated cylinder stat, there is a boiler thermostat which controls the maximum temperature of the output flow of the boiler. There is also a second over-temperature cutout in the boiler which requires manual reset and the usual over-pressure release valve in the boiler.

Even if all these safety devices in the primary circuit failed, there are the two safety over-temperature / over-pressure valves on the cylinder, i.e. there are five independent safety devices in total.

Surely then it is not a requirement to have two zone valves?

[Christian McArdle]

The wording requires the temperature measurement to be local. It specifically states "if the unit incorporates a boiler the thermal cut-out may be on the boiler". This suggests that an external boiler that is not incorporated may not use its cut-out to meet the requirement.

However, I've just examined the Megaflo installation instructions in detail. It appears that you can use just one motorised valve, if you use S-Plan and ensure that the zone valve power goes through both the overheat and normal thermostats. It is only necessary to have two valves if you use 'Y' plan, where the 3 port valve can't reliably isolate the cylinder. The systems I have seen have been 'Y' plan, so have needed the additional valve.

So it appears that you can just use the one valve for your S-Plan system. You just connect one switch wire to permanent live and the other to your boiler call for heat, in parallel with your heating valve.

Christian.

[FGoogle]

OK

So back to the original question

The wiring diagram for S Plan shows permanent live (on grey) and switched live from the timer (on Brown)

My Question was is there any reason I can't join the Grey wire to the Brown?

Anyone?>

Thanks

Mark

[Ed Sirett]

The grey should be connected to a permanent live supply independent of the time controls. The oranges are then connected to together and sent to the boiler's switched live input.

[Or alternative the 2 greys and 2 oranges from both valves are connected together to form one pair which switches the boiler form the boiler's supply.]

you're not it's the installation that's wrong.

- Ed Sirett - Property maintainer and registered gas fitter. The FAQ for uk.diy is at

Gas fitting FAQ CH FAQ a Boiler FAQ Fitting Standards Docs here:

[Ed Sirett]

There is a good reason:

Firstly the Zone valves are often used in pairs (one for HW & one or more for heating). If you connect the grey to the brown you will cause the zone valve to latch in the on state until _all_ zones are satisfied.

It does not matter if the HW cylinder is nowhere near the heating zone valve if the orange wire is live (because some zone valve somewhere is open) then this zone valve will stay open because the brown wire (which opens the valve) is connected to grey and (via the switch in the valve) to the orange and so the live.

[Christian McArdle]

What you do is have the zone call for heat (i.e. output from programmer and through any thermostats) to the brown wire. You have neutral on blue. You have permanent live on one of the other two (i.e. grey) and the boiler call for heat on the remaining one (i.e. orange?). It MUST be a permanent live. You can't cheat and use the brown instead. It won't work, as the other zone will then be able to turn on the other zone valve. This is dangerous and illegal, as the unvented cylinder will overheat.

Christian.

[Ed Sirett]

Time to get some pro help.

[allwaysaway]

replying to FGoogle, allwaysaway wrote: An old post but often thought the same thing, Can`t see what the problem would be as your still using micro switch and proven open valve. the switched live goes straight back to boiler via wiring centre as would permanent supply regardless of other motorized valves

[John Rumm]

Indeed it is. That means we have not the faintest idea what you are talking about because we can't see the original posts you are replying to; they expired from our news server long ago.

Please do us the courtesy of quoting some of the message you are replying to.

(the web site you are using even lets you do it automatically - just highlight a section of the message before you start typing your reply!)

[GeoffB]

replying to John Rumm, GeoffB wrote: I've recently replaced a faulty Honeywell V4043H motor. While investigating the wiring etc. to see how the whole S Plan system worked, I found myself asking the same question: why not connect the grey wire (normally permanently live) to the brown wire, on each of the two (HW and CH) zone valves? If you do that, the only connection between the two valves is the orange wires that feed live to the pump & boiler. For each of the zone valves, the brown and grey would go live together when switched on by the timer. But there must be a reason why the grey wire is permanently live , otherwise Honeywell would just have bridged the brown & grey in the valve.

[ARW]

Welcome to 2018

It is to stop back feeding through the programmers single pole relays.

If both CH and HW are calling and the programmer stops calling for say CH whilst in demand the live demand from the HW will keep the CH 2 port valve open.

[Mike Humphrey]

No, it wouldn't work. Consider the situation where both CH and HW call for heat. Both valves motor on, opening the valves and closing both microswitches to energise the orange wires, so the boiler runs. Then, the HW stops calling for heat. The thermostat no longer supplies power to the brown (and grey) wires. However, because the microswitch is closed, power flows from the orange wire (energised from the other valve's orange) to the grey. The grey is connected to brown, so brown is still energised, and the valve stays open. The system continues to heat the hot water when not required. If the CH stops calling for heat earlier, the same applies in reverse.

Mike