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Discuss Installing a Mira Platinum duel ceiling outlet shower in the DIY Plumbing How-To Guides area at PlumbersForums.net

Just purchased a Mira Platinum shower (dual ceiling fed high pressure/combi boiler version), which will be installed in the loft directly above the shower area in a bathroom that I am refurbishing.

I've read through the installation manual and a couple of things aren't too clear:

1. A couple of push fit isolating valves are supplied in the kit, to be fitted to the hot and cold water inlets (to the digital unit). However, on page 13 it states "We strongly recommend that full bore outlet isolation valves are fitted as close to the product as possible for ease of service and maintenance." I don't see the point of doing this. If I need to work on the feed to the shower heads I would simply use the hot and cold water inlet isolating valves to cut the water feeds, so why would more isolating valves be required on the outlets?

2. On Page 18 is shown "Typical Examples of Poor Plumbing..." and this includes "(Don't) Install the Digital Mixer Valve onto shared water supplies". This is shown in the following diagram:

Shared water supply.JPG

I appreciate this is the diagram for the bath feed installation, rather than the dual shower heads, but it shows the supply being teed from some existing hot and cold water supplies. There are already a number of hot/cold pipes in the loft running to a loft en-suite bathroom and I was planning to feed from these by teeing into them, but this examples suggests that shouldn't be done, or am I missing the point? How else can a hot/cold supply be provided? Even running new pipes from the source of the supplies would require teeing into some pipes somewhere in the system!

FYI: My hot water is via an unvented cylinder, under mains pressure, reduced to 3 bar. A Vaillant ecotec 637 system boiler heats the water. The cold water mains supply is also reduced to 3 bar.

Thanks in advance and a merry Christmas and Happy New Year to all who help people like me on these forums. I value your knowledge and advice.
 

moonlight

Plumber
Gas Engineer
Advent Win
A full bore valve will enable you to take out the whole unit if necessary and will not restrict the flow as an ordinally service valve will.
The drawing you have posted is for a pumped version of yours. Look at an image in your instructions for a mains fed supply's.

Page 14 of your instructions.
 
Hi moonlight thanks for posting.

A full bore valve will enable you to take out the whole unit if necessary and will not restrict the flow as an ordinally service valve will.
I agree that a full bore valve is better however, I don't understand why it is suggested to fit this on the "outlet" side of the digital valve. It is required to fit the supplied isolation valves on the inlet side (I suspect these aren't full bore - they don't look big enough), so surely if it was necessary to do some work on the outlet side, maybe replace the shower head(s), or even replace the pipes, turning off the inlet isolation valves would be sufficient to isolate the water supply from the outlet piping? Given that the ceiling fed pipes will be within 50cm of the valve I can't see any benefit to installing additional isolation valves.

The drawing you have posted is for a pumped version of yours. Look at an image in your instructions for a mains fed supply's.

Page 14 of your instructions.
The instructions show three "Typical Suitable Installations":
1. Instantaneous Multipoint Water Heaters and Combination Boilers (Page 14 - as you have mentioned).
2. Mains Pressurised Instantaneous Hot Water Shower, Heated from a Thermal Store (Page 16).
3. Gravity Fed Showers (Page 17).

I think my setup is more similar to 2, than 1 as the hot water is under mains pressure. Which suggests the diagram on page 16 is more representative of having an unvented cylinder storing the hot water.

Not that it really matters as the diagram I was referring to is in the "Typical Examples of Poor Plumbing and Installation Practices" on page 18, which I believe applies to any of the 3 "Typical Suitable Installations". I may be wrong as it isn't very clear. In this section it states "DO NOT: Install the Digital Mixer Valve onto shared water supplies". I'm not sure what this means or if it only applies to the Gravity Fed type of installation (I suspect it does) as at the end of the Gravity Fed Showers section it states "It is therefore best practice to have independent hot and cold supplies to the Low Pressure (pumped) Digital Mixer Valve".

So, I'm still confused about what the installation instructions are trying to tell me, but I don't think they apply to my setup.
 

moonlight

Plumber
Gas Engineer
Advent Win
You are right page 16, but that is not what you have either. you dont have a thermal store. The literature is not clear. I put full flows on the inlet, usually lever valves as easy to isolate, as you say no real point on the outlet. The plastic ones are difficult to turn off and often leak.


Mains pressure unvented
You will know you have this system if: you have a boiler the size of a small kitchen cupboard somewhere in your house.
An unvented mains pressure system stores mains pressure water in a large strengthened hot water tank (cylinder), usually found in the airing cupboard. The hot water will be heated either by immersion heaters fitted in the side of the cylinder or by a central heating boiler. This type of system doesn't require a cold water tank (cistern) in your loft and provides a high water flow rate & pressure. Other systems also producing hot water at mains pressure are available these are generally known as thermal store systems.
To make the best use of the flow & pressure of these systems we would recommend a digital or mixer shower. Alternatively, for a more gentle flow rate you could use one of Mira's eco mixer showers or fit an electric shower to the cold mains, this is an ideal low cost option for a second or en-suite shower room.

Connection to mixer instead of directly to shower
1577129094444.png
Post automatically merged:

If you have a multiblock on your cylinder you might be able to take a balanced cold supply?
 

EvilDrPorkChop

Gas Engineer
Advent Win
Hi moonlight thanks for posting.



I agree that a full bore valve is better however, I don't understand why it is suggested to fit this on the "outlet" side of the digital valve. It is required to fit the supplied isolation valves on the inlet side (I suspect these aren't full bore - they don't look big enough), so surely if it was necessary to do some work on the outlet side, maybe replace the shower head(s), or even replace the pipes, turning off the inlet isolation valves would be sufficient to isolate the water supply from the outlet piping? Given that the ceiling fed pipes will be within 50cm of the valve I can't see any benefit to installing additional isolation valves.



The instructions show three "Typical Suitable Installations":
1. Instantaneous Multipoint Water Heaters and Combination Boilers (Page 14 - as you have mentioned).
2. Mains Pressurised Instantaneous Hot Water Shower, Heated from a Thermal Store (Page 16).
3. Gravity Fed Showers (Page 17).

I think my setup is more similar to 2, than 1 as the hot water is under mains pressure. Which suggests the diagram on page 16 is more representative of having an unvented cylinder storing the hot water.

Not that it really matters as the diagram I was referring to is in the "Typical Examples of Poor Plumbing and Installation Practices" on page 18, which I believe applies to any of the 3 "Typical Suitable Installations". I may be wrong as it isn't very clear. In this section it states "DO NOT: Install the Digital Mixer Valve onto shared water supplies". I'm not sure what this means or if it only applies to the Gravity Fed type of installation (I suspect it does) as at the end of the Gravity Fed Showers section it states "It is therefore best practice to have independent hot and cold supplies to the Low Pressure (pumped) Digital Mixer Valve".

So, I'm still confused about what the installation instructions are trying to tell me, but I don't think they apply to my setup.
The isolation valves on the outlets are for if the box needs to be changed in the future (Which they will as they always fail the Digital boxes, i'm personally not a fan). It's so it can be easily changed by an engineer without getting water everywhere.

In terms of the 'Shared Supplies' as you say it's referring to a gravity fed system and doesn't apply to your situation.

In your situation you just need to take a hot supply from the hot pipework and a balanced cold supply to the box (As Moonlight says). Your existing cold supply you have in your loft may already be balanced from the Combination Valve on the cylinder, however you need to check this. If not you'll ideally need to run a cold pipe back to wherever your cylinder is to do the balanced cold supply.
 
The isolation valves on the outlets are for if the box needs to be changed in the future (Which they will as they always fail the Digital boxes, i'm personally not a fan). It's so it can be easily changed by an engineer without getting water everywhere.
As the box will be installed in the loft space directly above the shower area, both ceiling pipes to each shower head will be feeding water vertical down, so it would be fairly easy to ensure any water in these pipes is emptied (into the shower) and so I don't see a need for any isolation valves on the outlet connections. If the digital box was installed under a bath i.e. below the shower heads and the water was fed up the pipes, I could see then the isolation valves on the outlets would be useful.

Do you know if the supplied push fit valves are full bore? They don't look "thick" enough to be. If not, I assume full bore isolation on the inlet pipes possibly doesn't make any difference to the flow as it would need to be mixed first in the digital box. As our loft was an "extension" all the hot and cold piping is in plastic, so due to the inserts, would be more restricted than the copper pipe that runs through the rest of the house. I guess what I'm saying is that the plastic piping isn't going to give as good a flow as copper piping anyway. As part of the bathroom refurbishment, it would be possible for me to replace the plastic pipes feeding hot and cold water into the loft with copper pipes and then take these directly to the digital box, with the existing sink, toilet and bath continuing to be fed from plastic pipes. Not sure if the amount of effort to do this would warrant the difference in flow (if any)?

In terms of the 'Shared Supplies' as you say it's referring to a gravity fed system and doesn't apply to your situation.

In your situation you just need to take a hot supply from the hot pipework and a balanced cold supply to the box (As Moonlight says). Your existing cold supply you have in your loft may already be balanced from the Combination Valve on the cylinder, however you need to check this. If not you'll ideally need to run a cold pipe back to wherever your cylinder is to do the balanced cold supply.
If you have a multiblock on your cylinder you might be able to take a balanced cold supply?
There is a 3.5 bar pressure reducing valve feeding cold water to the unvented cylinder and a separate 3.5 bar PRV on the cold supply to the house taps etc. I guess this therefore means the hot and cold are balanced?

We have used thermostatic mixer showers for many years and these have worked well, with good pressure.
 

moonlight

Plumber
Gas Engineer
Advent Win
If you are not G3 qualified you shouldn't touch the valve. If you have a balanced supply connected from the valve that's where you can take your cold from. A picture of your valve would give a better idea of what's in your airing cupboard.
 

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