Zone valves for unvented cylinders

[Onetap]

3.22 mentions 'package' and 'components' and 'should'. This does not state that any particular component has to be used.

The appropriate standard is satisfied by compliance with 3.21 through the built-in safety devices.

As you say, the 2 port valve is there so you can tick a couple of boxes.

You are applying an innovative interpretation to avoid admitting that you were mistaken.

The word “should “ is used in 3.22, which is in the section of the G3 document headed ‘G3: Hot Water Supply and Systems: Guidance’. My understanding of 3.22 is that you should adhere to it’s recommendations in order to ensure you comply with the preceding section, headed ‘Hot Water Supply and Systems: The Requirement: G3’.


The probable reason why the Regulations require the use of the 2-port valve supplied, and leave no room for the discretion of a domestic plumber to select a suitable control valve, is because there are some 3-port valve types which are not suitable for this application. Rotary shoe 3-port valves suffer some leakage through the closed-off port; plug type 3-port valves are mostly only suitable for installation as mixing valves, not as diverting valves and should be fitted in the return. The installation of an appropriate 3-port valve does not ensure that any future replacement will be identical or equally suitable.

The 2-port valve supplied with unvented cylinder package has been selected by the manufacturer and is suitable for the recommended temperatures and pressures. Any other controls (say a modulating valve) should be fitted in addition.

 

[Bodd]

Bodd, part of the reason I asked is that you should register for the CC and get some more specific and in depth advise from a bigger group of Pro's.

Thank you Dan

I thought black and white we had to use the two ports but there is conflicting advice hear. I think the best thing I can do is talk to Vailant again, as I do think the Mi's are gospal.

Thanks again

Bod

 

[mysteryman]

G3 does not specify anywhere that there has to be a 2 port valve. All it asks for is a device to shut off the source of heat. This device can be a thermostat and it can operate on a relay or valve, and the device can be on the boiler.

 

[Dan Robinson]

G3 does not specify anywhere that there has to be a 2 port valve. All it asks for is a device to shut off the source of heat. This device can be a thermostat and it can operate on a relay or valve, and the device can be on the boiler.

The boiler primary flow and return connections should be made to the unit. The motorised valve
must be fitted into the primary flow.

5.2 INDIRECT THERMAL CUT-OUT AND 2-PORT MOTORISED VALVE
To comply with Building Regulations and to prevent the Megaflo from overheating the 2-Port
motorised valve supplied MUST be fitted to the primary flow to the indirect coil (see Diagram 10).

Annoying but, it means that we have to comply. MI's superceed everything else.

 

[mysteryman]

Box ticking. Let's revolt!

 

[Dan Robinson]

I heartily agree!

 

[Onetap]

G3 does not specify anywhere that there has to be a 2 port valve. All it asks for is a device to shut off the source of heat. This device can be a thermostat and it can operate on a relay or valve, and the device can be on the boiler.

You do whatever you like.

The 2-port valve that is usually (always?) supplied with unvented cylinders is a Honeywell V4043; this is normally closed, it motors open and is shut by the spring-return in the event of a power failure. It fails to the safe position.

In Bodd's case, the designers intend to use a 3-port valve (see the frst post). The 3-port valve frequently encountered is the mid-position valve, a Honeywell V4073A, or similar. You cannot use one of these valves because the hot-water port is normally open. In the event of a power failure, it will spring-return to the open (to DHW) position. It fails to an unsafe position. See the second post. It would be interesting to know which valve they propose using.

With regard to your interpretation of G3, the energy cut-out device is referred to in the Guidance clauses 3.21 and 3.18. The energy cut-out could be on the boiler (3.21) , but it has to shut down the boiler in the event of the storage system overheating (3.18 ), not the boiler. Don't tell me how you'd interpret that, that is just what is says.

 

[gaswizzard]

Wire all system controls through OH stat , job done.

 

[mysteryman]

If the primary heat source is a boiler, the cylinder can't overheat without the boiler overheating. A limit 'stat on the boiler prevents this. Clause 3.21 complied with. Job done.

 

[Onetap]

Clause 3.21 complied with. Job done.

Just clauses 3.18a and 3.22 contravened.

 

[mysteryman]

Not so.

3.22 states [as above]: 'should be appropriate to the circumstances in which they are used'. Nowhere does G3 say you have to have a 2 port valve. These clauses are in any case in the Guidance - they are not the legislation.

Clause 3.18a is 'all systems' which includes immersion heaters, for example, whereas 3.21 is specific to cylinders heated by boilers - which is what we are discussing here.

I am not advocating a dangerous or even an illegal installation. Just one which is adequately protected without superfluous [and detrimental] components.

Compliance with clause 3.21 is safe, adequate and legal.

Adding anything else is box-ticking to no other purpose.

 

[Onetap]

Not so.

3.22 states [as above].

3.22 requires the use of a hot water storage system or package. The 2-port valve is a part of that package and cannot be omitted. The manufacturers' installation instructions specify the 2-port valve is to be fitted. There is no scope for any innovation or interpretation of this. It is box ticking, if you like to call it that; the legislation is there to protect consumers from installers who think they are clever. The G3 certification is for Installers.

If you want to get into design, there is provision in 3.26 for systems of >500 litres; such design is to be done by an 'appropriately qualified engineer'. A G3 ticket is not an 'appropriate qualification'.

I wonder why you are so insistent that the 2-port valve is unnecessary; the valve is free, it comes with the water heater, it will be fully open in normal operation and so could be used in conjunction with other control devices.

What do you do with the 'superfluous' 2-port valves from unvented cylinder packages that you fit? E-Bay?

 

[Dan Robinson]

I wonder if screwing the valve to the side of the tank and just using the microswitch would comply ?

 

[mysteryman]

Who says it can't be omitted? The relevant phrase in clause 3.22 is:

"The package and components should be appropriate to the circumstances in which they are used and should satisfy an appropriate standard that will ensure the requirements of G3(2) and G3(3) will be met."

A cylinder heated by a boiler with on-board limit devices complies with G3 clause 3.21.

We all seem to agree that it is the cylinder manufacturers who are driving the fitting of 2 port valves to all unvented cylinders - regardless and heedless of need. They are not free - you pay for them in the price of the cylinder. They are not necessary. They add complication, they are another item to break down, and worst of all, they obstruct pump overrun, which is wasteful of energy and damaging to the pump.

 

[Onetap]

You didn't answer the question.

What do you do with the 'superfluous' 2-port valves from unvented cylinder packages that you fit?

E-Bay?

Who says it can't be omitted?

I do. The valve is a part of the package and if you omit it, the BBA and BS certification is invalidated. I have a CITB manual, 'Unvented Hot Water Storage Systems'. There is an example installation checklist in the appendices. This includes the statements;

"Is the unit or package certificated e.g., BBA, WRC or equivalent."
and " Indirectly-fired thermostat, energy cut-out and zone valve fitted?"


I say again; the G3 certificate is for an "Installer". It is not for a designer nor for someone who thinks he can purloin components from the package that the customer has paid for, because he deems them to be 'superfluous', and then signs a false declaration regarding the cylinder installation being an approved package.

"The package and components should be appropriate to the circumstances in which they are used and should satisfy an appropriate standard that will ensure the requirements of G3(2) and G3(3) will be met."

That is probably a reference to the manufacturers requirements about temperatures, pressures, protection from water, etc.. 'An appropriate standard' is the BBA, BS, WRC certification that you invalidate by omitting the zone valve.

They are not free - you pay for them in the price of the cylinder. They are not necessary. They add complication, they are another item to break down, and worst of all, they obstruct pump overrun, which is wasteful of energy and damaging to the pump.

The client pays for them. See the unanswered questions above. Do you give the client a refund in respect of the 'superfluous' 2-port valves that you don't fit? If you omit the 2-port valve, which control valve do you use?

They won't obstruct pump over-run if the system is competently designed.