Zone valves for unvented cylinders

[Onetap]

If II followed the schematic the boiler two fires and a Arger would be supplied by a 22mm gas supply.

I'd suggest you do a quick estimate of the size of the gas pipe and submit a written query, keeping a copy. I'd also keep a copy of the schematic and check any specification for any clauses requiring you to check pipework sizes. Keep a copy of the schematic, because they'll be looking for someone to blame if they've cocked it up.

You still can't install the cylinders without the 2-port valves, regardless of what their schematic says, there must be something to control the cylinder temperature.

 

[Bodd]

Maybe the UV cylinders being supplied are pre plumbed units.

No they come just a basic unit I have piped them up via the two ports.

 

[Onetap]

I'll do it to their design as long as I don't compramise the regs..

You can't, it would; you can't omit the 2-port valves.

As an example, the installation instructions for the Vaillant Unistor unvented cylinder state;

5.4.1 Primary pipework
To prevent the uniSTOR from overheating the 2 port motorised valve supplied with the boiler (cylinder; bad translation from German ) must be fitted to the primary flow to the indirect coil (see figure 5).

You must fit it; end of. Every other unvented cylinder will have a similar clause in the instructions.

What would an Electrician say if their designer wanted him to run a power supply from the distribution board without any fuses or MCBs?

 

[Agile]

They are Building services & Environment consultants.

So am I. They're wrong.

Those that can do; those that can't become consultants.

Does that apply to you too?

 

[Onetap]

Does that apply to you too?

Yep. I knew some smartarse would query that.

 

[Dan Robinson]

Bodd - I have to ask.... Are you G3 qualified and Gas Safe registered?

 

[mysteryman]

It is amazing how people follow the mantra of 'you MUST fit a 2 port valve'.

Try reading the G3 regs carefully. They do not state anywhere that you have to have a 2 port valve. They state that an energy cut-off device has to be used; they state that there is no specific correct route to achieving safety, and that alternative methods may be used. One clause, however, is clear:

Clause 3.21 reads: If the primary heat source to an unvented storage system incorporates a boiler, the energy cut-off may be in the boiler.

Energy cut off here clearly means an overheat or limit thermostat.

Later on there is mention of the energy cut-off 'acting upon a device such as a relay or motorised valve to shut off the source of energy to the storage system'.

 

[Dan Robinson]

I agree, yet.... annoyingly most cylinder MI's state a two-port valve and as we know, MI's superceed everything else.

 

[mysteryman]

They are just covering their backs - and forcing you to buy kit you don't need.

 

[Onetap]

It is amazing how people follow the mantra of 'you MUST fit a 2 port valve'.

Try reading the G3 regs carefully. They do not state anywhere that you have to have a 2 port valve. They state that an energy cut-off device has to be used; they state that there is no specific correct route to achieving safety, and that alternative methods may be used.

ISTR the BBA certification is provided for the cylinder and all the components supplied with it; if you omit the 2-port valve, the certificate is not valid. You could devise a system which was equally safe without the 2-port valve, but it wouldn't have the BBA test certification. The G3 installer's certification cover you for installing, not designing, unvented systems.

 

[Bodd]

Bodd - I have to ask.... Are you G3 qualified and Gas Safe registered?

Dan

I am gas safe and I was one of the first to pass my unvented with bpec number 12 .
I don't know everything and I do come on hear for advice. I have questioned alit this firm s design they would have me follow. But I would be a fool if I just dismissed them and did no resurch of my own.
Have I said anything that suggests I don't know what I'm talking about?
I'm never to proud to admit I'm wrong or ask for advice.

It's just nice to hear people make me right.

Bod

 

[mysteryman]

The issue here is whether you are ticking boxes, or installing a safe and effectively controlled system without unnecessary gizmos.

A boiler with a non-self-resetting overheat device [limit 'stat] is perfectly safe and complies with clause 3.21 of G3. The best boilers have also a non-self-resetting flue temperature overheat device, so they have double protection. These boilers comply fully, and other external bits such as 2 port valves are not required by G3.

The other major disadvantage with fitting a 2 port valve, further to the extra cost, complication, and risk of failure, is that it can choke off pump overrun.

 

[Onetap]

The issue here is whether you are ticking boxes, or installing a safe and effectively controlled system without unnecessary gizmos.

A boiler with a non-self-resetting overheat device [limit 'stat] is perfectly safe and complies with clause 3.21 of G3.

Read clause 3.22.

http://www.planningportal.gov.uk/uploads/br/100312_app_doc_G_2010.pdf

"3.22 Any unvented hot water storage system up to 500 litres and less than 45kW should be in the form of a proprietary hot water storage system unit or package."

The 2-port valve is a part of the package and cannot be omitted without invalidating the BS and/or BBA certifications. Generally, you do not have the option of amending the packaged system, regardless of how clever you might think you are.

Your suggestion of using a thermostat on the boiler is only relevant if the OP's system is more than 500l or 45 kW.

 

[mysteryman]

I am obliged to you for posting the complete document. You had not quoted even the whole of clause 3.22, and I had got 3.21 slightly wrong from memory. Here they both are:

3.21 If an indirect supply of heat to an unvented hot water storage system incorporates a boiler, the energy cut-out may be on the boiler.

3.22 Any unvented hot water storage system up to 500 litres and less than 45kW should be in the form of a proprietary hot water system unit or 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 G2(2) and G3(3) will be met (eg BS EN 12897...etc)

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.

 

[Dan Robinson]

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.