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Discuss Joining two cold water tanks together in loft. in the Bathrooms, Showers and Wetrooms area at

  1. Wrighty8

    Wrighty8 New Member

    Thanks again fellas, some quality debate there and great advice.

    I am aware of the extra weight and it will be over a supporting wall and 18mm ply.

    I was also aware of the cold water feed to the shower being below the other outlet.

    Great thread, hopefully it helps others when they do the same!
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  2. Jim Goodenough

    Jim Goodenough Plumber

    This is probably only theoretical now but is it best practice to link CWS tanks with 35 or even 42mm (gets expensive I know)?
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  3. Ric2013

    Ric2013 Plumber Top Contributor!!

    What I find odd is that my reading of the WRAS 'blue book' makes it seem that it is a requirement to have two float valves, yet City and Guilds textbook for level 2 shows one valve, two interlinks (one high, one low) in wide-bore pipe to a second tank, and main draw off from the second tank.

    Personally, the City and Guilds approach strikes me as a better arrangement as I suspect it could be difficult to ensure that the two float valves remain in perfect sync (and because an extra valve seems like a waste of resources), but I've not yet come across an interlink arrangement, nor had to construct one, so this isn't based on experience.
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    CHRISX Active Member

    Hello Ric2013,

    Thanks for describing the WRAS specification and the City & Guilds version regarding linking 2 x CWS Tanks.

    Fitting 2 x Floatvalves will ensure that there is not a `layer` of water at the top of either CWS Tank that is not Oxygenated - the Floatvalves would not have to be in perfect sync. although they would both operate together.

    Regarding you mention of `an extra Floatvalve seeming like a waste of resources` - fitting an additional Floatvalve would be less expensive than connecting the Tanks with 28mm or 35mm pipe at High / Mid level.

    There is also another practical / leak prevention reason for NOT fitting the High / Mid level connections as I describe below.

    As You know the idea of linking the Tanks at High / Mid level is to prevent the upper level water from stagnating - but in my opinion that is an inappropriate option both in Materials cost / additional unnecessary work and the possible vulnerability of the High / Mid level Tank connections.

    Compare the cost of that in this example: 2 x additional 28mm or 35mm Tank Connectors & washers and the 28mm or 35mm Tube plus additional work - with the second Floatvalve option of: an additional Floatvalve - Servicing valve - Tap connector - 15mm Tee & piece of 15mm Tube plus additional work.

    Also with the `City & Guilds version` even with Us Expert Plumbers - depending upon the Shape and Quality of the CWS Tank there is always the possibility that the High / Mid level connections would experience some `Flexing` when large / Pumped draw-off`s were occurring [or on the initial filling process] making those connections a possible weak point for future leaks.

    There are NONE of those extra work / unnecessary costs / possible future leaks problems if 2 x Floatvalves are fitted.

    And that guarantees that all water entering the CWS Tanks is Oxygenated whereas I am NOT convinced that a High / Mid level connection between the Tanks would transfer enough Oxygenated water into the `Secondary` Tank to prevent a layer of less Oxygenated water existing.

    As the Water level was falling and rising in the Tanks I feel that very little Oxygenated water would be flowing between the `Main` Tank and the `Secondary` Tank through the High / Mid level pipe link.

    I am attaching a WRAS illustration of 2 x CWS Tanks connected together.



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    Last edited: Mar 8, 2018
  5. TonyC

    TonyC GSR

    If installing linked tanks as per the suggested WRAS illustration it is essential that both floats are set at the same height.
  6. YorkshireDave

    YorkshireDave Plumber Top Contributor!!

    I am assuming here that 'feeding a shower' means via a pump.

    Personally, I would repipe the CW feed to the cold taps so it was mains fed. This is not only far more safe & hygenic but then you only need one ball valve on the tank opposite the supplies to the pump.

    The rate of discharge from the pump will guarantee mixing so the stagnation issue (far more pertinent when feeding cold taps) goes away.

    Always choices...

    CHRISX Active Member

    Hello YorkshireDave,

    I agree with You that at least the Bathroom Basin Cold Tap should be piped to the Mains - that supply's more hygienic water for Tooth brushing irrespective of the `Potable water` Bylaw 30 is supposed to ensure regarding the CWS Tank water quality supposedly being `Drinking water quality`.

    Mains water direct from the pipe at a Bathroom Basin is definitely better.

    Also if the Householder knows that they have Mains water to the Basin they can take drinking water from there.

    I did that in my Home [30 years ago] and I have been advising Customers to have Mains water to their Bathroom Basins when I carry out a Re-Plumb of a property for the last 30 years.

    I cannot agree with You or any Member / Plumber that there should only be one Floatvalve fitted when 2 x CWS Tanks are joined together in any circumstances.

    As I have mentioned in every one of my messages on this thread - the cost of fitting a second Floatvalve is negligible and it guarantees that ALL of the fill water is Oxygenated in both Tanks.

    ANY other configuration would be Inferior to that and would probably cause the `Secondary` CWS Tank water to at the very least NOT be `potable` even if actual `stagnation` did not occur.

    Why would any Plumber just fit one Floatvalve to 2 x CWS Tanks and `Hope` that large water draw-off`s would cause Oxygenated water to flow to the Secondary CWS Tank via a pipework link at the bottom of the Tanks ?

    Unless both Tanks are almost drained I know that there will be an `upper layer` of water in the Secondary` CWS Tank would just move up and down the Tank when water is being drawn off - that `layer` would not Mix with or receive Oxygenated water from the `Main` CWS Tank.

    As I have mentioned Bylaw 30 above - although the Tank Insulation is to prevent the Tank water from either Freezing or `Heat gain` - during warm weather the `upper layer` of water in the `Secondary` CWS Tank WILL warm up in comparison to the incoming Mains water temperature and that will help to maintain the upper layer stratification situation.

    That slightly warmer upper layer of water will remain `floating` on top of the colder water that would come in from the `Main` CWS Tank at the bottom of the Tank - unless as I mentioned there are very large draw-off`s of water - by which I mean that both Tanks are almost emptied.

    However IF that amount of draw-off is required where the Tanks are almost emptied irrespective of the Floatvalve filling - it would mean that the CWS Tanks storage was still not large enough even with 2 x Tanks linked.


    Last edited: Mar 10, 2018
  8. YorkshireDave

    YorkshireDave Plumber Top Contributor!!

    Hmm. I fully accept that regulations exist generally to protect people. One should comply. However, you knew that was coming, your essential premise that tanks permanently contain stratified layers is flawed.

    Firstly, the stratification you describe depends on very specific hydraulic loading, temperature conditions and flow characteristics. Outside of a narrow model it simply cannot occur. I would suggest that might be at best 5% of the time, but of course that depends on each installation.

    Secondly, that stratification can only exist for a very limited time physically. Once temperature equilibrium occurs that naturally mixes the layers.

    Lastly, in all my years I have never, ever, been able to synchronise float valve operation. As close as I have got, they have never maintained any level of closeness of sync either. We are talking here of poorly produced products (even the likes of Pegler) and with such imprecision they drift quickly and far. Rather than risk failure, I have concluded one is better (tank connections notwithstanding) as my own responsibility to my customers is pragmatic as opposed to a purity of compliance.

    Perhaps we might agree to differ?

    CHRISX Active Member

    Hello again Yorkshire Dave,

    Thanks for your reply.

    I am not trying to cause / prolong an argument between Us - but just to comment on a couple of your points:

    I was fitting 2 x Floatvalves in Twin CWS Tank installations YEARS before even the 1987 Water Bylaws were introduced. - I have not just been `conforming to the Water Regulations` - I have been installing 2 x Floatvalves because it is the BEST method of ensuring that both CWS Tanks are filled with Oxygenated water.

    I cannot see why ANY Plumber would not want to ensure that by fitting 2 x Floatvalves - it makes no sense to install Twin CWS Tanks any other way.

    The stratification that I described would exist because there would NOT be temperature equilibrium in the `Secondary` CWS Tank or a mixing flow from the `Main` CWS Tank.

    If we imagine an `average draw off` for a Bath or a Shower regarding the amount of Cold Mains water refilling the Tanks - the colder water which flows into the `Secondary` CWS Tank at low level from the Main Tank would NOT mix with the upper warmer layer of water - there would be a `Strata` of warmer water in the upper level of the Tank.

    Just as when the Cold Water feed to a Hot Water Cylinder enters at the bottom of a Cylinder the Hot water remains above the Cold - any mixing would be very slight at the bottom of the Hot water and there would be Stratification levels of various temperature Hot Water - the extent of which depending on whether the Cylinder was being heated by the Coil / a Boiler or an Immersion Heater.

    There would be that warmer upper layer of water in the `Secondary` CWS Tank because it would hardly ever be drawn off and the incoming Cold water would not mix with it.

    I accept that if no water was drawn off for perhaps 24 hours then there would probably be some temperature equilibrium within the `Secondary` CWS Tank however when the water started flowing in from the `Main` CWS Tank and that water became colder than the water in the upper layer of the `Secondary` CWS Tank the stratification would begin again.

    With regard to `synchronising the 2 Floatvalves` why would absolute precision be such a necessity ?

    Obviously it is important that the Floatvalves are fitted to the CWS Tanks at exactly the same height and that the Floats are located on the valve arm at the same point - when installed as such the Floatvalves are `synchronised` well enough.

    If the Floatvalves are NOT fitted as above then there might be some strain on the valve arm of the lowest Floatvalve because the Float would be lower in the water than it should be - but unless there was a big difference in the height it should not cause a problem with premature indenting of the Floatvalve washer and the subsequent dripping that might cause.

    Just my thoughts on your comments - I am pleased to correspond with a fellow Professional - but as You wrote `We will agree to differ` on the subjects of the Floatvalves / Stratification etc.


    • Like Like x 1
    Last edited: Mar 10, 2018
  10. DAVE01

    DAVE01 Member

    Hello A Better way would be to Connect Ballcock as is and conection between two tanks is ok But Make sure you take all Water Conections out of the tank without ballcock if you do it your way you could get stagnent water and no need for two overflows take over flow out of tank with ballcock
  11. CHRISX

    CHRISX Active Member

    Hello DAVE01,

    I am not trying to start an argument - I am just trying to find out why some Members are trying to insist on advising inferior / possibly unhygienic methods of installing 2 x CWS Tanks ?

    How is what You described better than fitting 2 x Floatvalves and guaranteeing that there will NEVER be a problem with Stagnation or the water in one of the CWS Tanks becoming no longer `Potable` ?

    While the method of installation that you described would be better than some configurations - no method that does not include 2 x Floatvalves is as good as an installation where 2 are fitted.

    If your method of installation was done on for example 2 x 50 Gallon CWS Tanks and for some reason the water draw offs were small for a period of time there could still be an upper layer / a Strata of water in the `Secondary `CWS Tank that just moved down and up in the Tank not mixing or getting Oxygenated.

    Obviously I know that 2 x 50 Gallon CWS Tanks would be installed to supply a quite high Domestic demand - but Property`s change ownership and another Family might not have such a high demand / use frequent large draw-off`s from the CWS Tanks.

    Having to add an additional overflow to the `Secondary` CWS Tank is also not prohibitive in terms of either Materials or Labour.


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    Last edited: Mar 11, 2018
  12. Ric2013

    Ric2013 Plumber Top Contributor!!

    ChrisX: although I disapprove of your use of bold type and capital letters, I can't help feeling I agree with you on this one.

    You missed my point on 'waste of resources' entirely. I place a higher value on the environment than on money so I did not intend 'resources' to mean money. But I do take your point in that four 35mm tank connectors etc etc probably contain more brass etc than two isolators and two ballcocks, not to mention the wide-bore pipe itself.

    To be fair, what you are saying (if I follow you correctly) about stratification also makes sense - the trickle of water from the valve in action will probably help stir the top stratum of water into the rest. That said, I have a suspicion that the risks associated with poor plumbing practices causing a multiplication of legionella are grossly exaggerated (which isn't to say I don't follow the rules myself).
    • Agree Agree x 1
  13. CHRISX

    CHRISX Active Member

    Hello Ric2013,

    Thanks for your message,

    I did think that You were referring to the Environment when you mentioned a `waste of resources` regarding fitting a second Floatvalve etc. and when I stated that it would be less expensive to install that the 2 x 35mm Tank connectors & washers plus a piece of 35mm Copper tube I should have worded that as something like:

    Fitting a second Floatvalve, Isolating valve, 15mm Tee and a piece of 15mm Copper tube would have less Environmental impact for producing those Materials than the impact for producing 2 x 35mm Tank connectors & washers plus a piece of 35mm Copper tube.

    With regard to 2 x Floatvalves preventing the Stratification that I have previously described - it is not just that `the trickle of water from the valve in action will probably help stir the top stratum of water into the rest` - every drop of water entering both CWS Tanks will be Oxygenated so the issue of Stratification / Stagnation would not exist.

    The risk of Legionella should be negated by not only the fresh Oxygenated water flowing into both Tanks but also because the Water temperature should never be high enough if the CWS Tanks are Insulated correctly to prevent `Heat Gain` as well as Freezing.

    I agree with You about the risk of Legionella in Domestic Properties being exaggerated with regard to poor Plumbing practices.

    In fact I know of a very large private Landlord who has instigated `Legionella Risk Testing` for all of their properties - at least 2,000 Homes - and those Tests are failing any Home that has a CWS Tank that does not adhere fully to the Bylaw 30 installation specifications - or where ANY Rust is found in a CWS Tank - of which there are many - that Landlord will then either have to replace the Tanks if they are very old or bring newer Tank installations up to the standards of Bylaw 30.

    That will no doubt cost them Hundreds of Thousands of Pounds - if not over a Million pounds - I have been told by Friends who carry out work for them that they were notorious for always trying to get the cheapest Repairs done in their properties - always trying to convince Contractors to `Do the cheapest job possible`.

    Because of their ignorance of the `Health & Safety Regulations` which do NOT call for `Legionella Risk Assessments` in Domestic Rented Properties they are committed to spending possibly over a Million pounds - most of which is probably unnecessary.

    I have read HSE Documents on the `Risk of Legionella in Domestic Properties` which state categorically that detailed Risk Assessments & Testing are NOT required in Domestic Properties - although obviously the Plumbing must be `Safe & Hygienic` [my wording] for people to use - meaning that possible issues such as We have discussed in this thread are prevented or rectified.

    Obviously We know that stored Hot water should be heated to 60 degrees and that long `dead legs` of pipework which are not in use should be removed to prevent any bacterial build up in water that basically does not move within the pipework for years but which could release bacteria into the pipework that has water flowing through it.

    EDIT: I should add for possible future readers that there are HSE Regulations which require `Legionella Risk Assessments` in Commercial / Industrial Premises.


    Last edited: Mar 12, 2018
  14. Ric2013

    Ric2013 Plumber Top Contributor!!

    Yes, I'd like to see the statistics for Legionnaires' disease. I've been told (by a degree educated mechanical engineer) that no one ever dies of Legionnaire's contracted in a domestic environment but that doesn't prove that they don't suffer from it, and it would be good to see this somewhere official.

    Sorry if I misread your comment on my comment, and thanks for the clarification.
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  15. CHRISX

    CHRISX Active Member

    Hello again Ric2013,

    I have not got the statistics about Legionaries Disease but here are some details from the HSE regarding whether detailed Legionella Risk Assessment & Testing is required in Domestic Properties:

    This has been Copied & Pasted from an HSE Document:


    Some consultants & letting agents misinterpreting landlords responsibilities regarding legionella risks to their tenants

    Some consultants and letting agents are using the revised L8 ACOP to suggest that new legislation has been imposed on landlords of domestic rented properties for managing and controlling the risks of exposure to Legionella bacteria of their tenants. This is wrong, the legislation has not changed and misinformation/misinterpretation can impose unnecessary financial burdens on landlords where they are being charged for legionella testing and certificates they don’t actually need.

    HSE Panel opinion:
    • There is a legal duty for landlords to assess and control the risk of exposure to legionella bacteria, but Health and Safety law does not require landlords to produce or obtain, nor does HSE recognise, a ‘Legionnaires testing certificate'.
    • Legionella testing (or sampling) is generally not required in domestic hot and cold water systems and then only in exceptional circumstances.
    • Misinterpretation of the legal requirements by some consultants and letting agents about landlords’ responsibilities to manage and control legionella in domestic premises may result in unnecessary financial burdens being placed on landlords and tenants.
    The law is clear that if you are a landlord and rent out your property (or even a room within your own home) then you have legal responsibilities to ensure the health and safety of your tenant by keeping the property safe and free from health hazards.

    Section 3(2) of the Health and Safety at Work Act 1974 (HSWA) makes provision for relevant health and safety legislation to apply to landlords to ensure a duty of care is shown to their tenants’ with regard to their health and safety.


    The above details / Information is what the Landlord that I mentioned in my previous message has completely misunderstood.

    Reading just the Information above could save them over a Million pounds if my Guesstimate of the cost of replacing the CWS Tanks in perhaps 1,700 of their `over 2,000 Properties` is anywhere close to the total cost.


    Last edited: Mar 12, 2018
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