GBEzine

1. • CommentAuthorShevek
   • CommentTimeJan 8th 2012 edited

    
   What type of plumbing situation causes the shower to change in pressure and/or temperature when others taps in the household are used? And how do you make sure to avoid it?
2. • CommentAuthorowlman
   • CommentTimeJan 8th 2012

    
   Pipework bore not big enough?, different hot and cold pressures? Perhaps.
3. •  
     CommentAuthorJSHarris
   • CommentTimeJan 8th 2012

    
   May just be the way the pipe runs have been laid. If the shower is on the end of the hot run, for example, then pretty much any tap that's opened on the hot run ahead of the shower will drop the shower hot pressure.
   Often the hot and cold runs will be different, adding to the likelihood of imbalance.
   
   One way to reduce the problem is to run separate hot and cold feeds to the shower from the point of origin in the house for each supply (tanks, combi boiler, mains feed etc). Provided the supply pressure is OK this will usually minimise the impact of other taps being turned on. If the supply pressure is low, then it may be that this is something you just need to live with, although the effect on shower temperature can possibly be alleviated a bit by using a thermostatic mixer. This won't be able to stop the shower temperature dropping if the hot supply pressure drops to far, but should stop the shower getting too hot when the cold supply pressure drops.
4. • CommentAuthorDarylP
   • CommentTimeJan 8th 2012

    
   Combi boiler.... ?
   
   As the taps are opened, the pressure that the combi 'sees' drops, so the hot water throughput drops. Our 1970s semi has an incomer in 15mm copper that has been creased, so the cold mains is restricted in terms of flow...
   
   It needs upgrading to 25mm Poly, when I get the time....
5. • CommentAuthorDantenz
   • CommentTimeJan 8th 2012 edited

    
   This is very much a normal characteristic of having a combi boiler so I assume this is what you have. There are ways to minimise this effect, pipe size being one of them but even then it will still happen to a degree. A combi boiler is fed with cold water straight off the mains water supply however, the water flow rate through the boiler is restricted down inside the appliance so that the hot water supplied to the taps can be sufficiently heated. Although the boiler produces hot water at mains pressure the actual pressure on the hot will always be less than the cold because of resistance and pressure drop of the water having to pass through the boiler hydraulics and heat exchanger. So, when another cold tap, toilet or hot tap is used when the shower is on will cause pressure and flow changes at the shower valve. Also water will always take the least line of resistance so easier for water to flow from a downstairs kitchen tap than a first floor tap. System can be balanced by installing ball-o-fix type valves in the supply pipe work at every outlet to equalise the resistance or the method I prefer is to put a pressure reducing valve on the cold mains but take the cold supply to the boiler BEFORE the reducing valve. This essentially gives you higher pressure on the hot than you have on the cold so the hot water flow is less affected when multiple outlets are being used.
6. • CommentAuthorJoiner
   • CommentTimeJan 8th 2012

    
   You don't need to have a combi to experience this problem. Opening a tap anywhere in the cold water system feeding an electric shower will reduce the pressure, the reduced flow causing the temperature to rise.
7. •  
     CommentAuthorSteamyTea
   • CommentTimeJan 8th 2012

    
   I have a pumped shower coming off the same header tank as the cylinder and never have this problem.
   Old house had a gas combi and one tiny drip from another taps used to turn the shower either too hot or too cold, hence I have a vented system now.
8. •  
     CommentAuthorjoe90
   • CommentTimeJan 8th 2012

    
   I have no problem with my shower because I designed it differently as I suffered from this problem in my last house.
   
   I have a DHW tank not combi. The shower hot connection is right next to the DHW tank outlet and the 22mm from the tank is split into two 15mm pipes, one for the shower and one for everything else.
   
   The cold feed to the shower comes from the cold tank in the loft, not the incoming main, and is seperate and below the other feed coming out of the cold tank which feeds the DHW tank (the reason for this is if the cold tank runs out of water for any reason the hot supply fails before the cold so you cant be scalded in the event of a failure)
   
   Because both hot and cold for the shower are fed from the cold water tank in the loft the pressure is balanced. You can flush any toilet, turn on any tap and the shower temprature stays completely stable. I am not sure this design would comply with regulations but it works and has a fail safe to protect you from scalding.
9. •  
     CommentAuthorJSHarris
   • CommentTimeJan 8th 2012

    
   <blockquote><cite>Posted By: joe90</cite>I have no problem with my shower because I designed it differently as I suffered from this problem in my last house.
   
   I have a DHW tank not combi. The shower hot connection is right next to the DHW tank outlet and the 22mm from the tank is split into two 15mm pipes, one for the shower and one for everything else.
   
   The cold feed to the shower comes from the cold tank in the loft, not the incoming main, and is seperate and below the other feed coming out of the cold tank which feeds the DHW tank (the reason for this is if the cold tank runs out of water for any reason the hot supply fails before the cold so you cant be scalded in the event of a failure)
   
   Because both hot and cold for the shower are fed from the cold water tank in the loft the pressure is balanced. You can flush any toilet, turn on any tap and the shower temprature stays completely stable. I am not sure this design would comply with regulations but it works and has a fail safe to protect you from scalding.</blockquote>
   
   Mine is now like this, although with a combi rather than hot tank and with mains water cold feeds, as I changed the pipework when we had the combi installed, which is why I suggested it as a possible fix earlier, although it did need some tweaking. Works like a dream now though, as we get virtually no effect on the shower from opening taps elsewhere. I did initially have a problem with the kitchen sink hot tap. If this was turned on full then it would cool the shower, because despite being on a separate pipe run it is much closer to the boiler. The fix (perhaps bodge) was to partially close the ball valve isolator on the kitchen tap, which reduces the maximum flow rate. The positive side effect of that has been less splashing and wasted hot water.
10. •  
      CommentAuthorjoe90
    • CommentTimeJan 8th 2012

     
    JSH, great mind's think alike!, just goes to show that a bit of common sense and practical knowledge is sometimes all that is needed to solve problems. Although easier for new build may be more difficult for existing builds without ripping it all out.
11. • CommentAuthorTimber
    • CommentTimeJan 8th 2012

     
    ^Essex flange and dedecated pipe work will sort it out!
12. • CommentAuthorqeipl
    • CommentTimeJan 8th 2012 edited

     

    Posted By: ShevekWhat type of plumbing situation causes the shower to change in pressure and/or temperature when others taps in the household are used? And how do you make sure to avoid it?

    
    
    If your hot water is at mains pressure (e.g. combi boiler or unvented cylinder) then you need to install what my supplier called a 'groupset' - which appears to be a pressure balancing valve on the mains supply.
    One output from the groupset goes into the combi boiler (or unvented cylinder) and the other is a dedicated cold water supply to the showers.
    All other cold supplies (toilets, basins, etc.) are fed from a separate branch of the mains that is upstream of the groupset.
    This gives you mains pressure showers while ensuring that the hot and cold pressures at the shower mixer are always balanced. If someone flushes a toilet or opens a kitchen tap it has no effect on the cold pressure at the shower.
    
    If your DHW cylinder is of the vented type then joe90's system sounds very sensible.
13. • CommentAuthorTerry
    • CommentTimeJan 8th 2012

     
    Same as qeipl - except our supplier did call it a balancing valve
14. • CommentAuthorCWatters
    • CommentTimeJan 9th 2012

     
    Is it a mains pressure or vented hot water system? Can be lots of different reasons not all applicable to both types..
    
    Long/wrong bore pipe runs around the house
    Long/wrong bore pipe from main to house
    Scaled up pipes
    Isolation valve not fully open or not a full bore type
    Poor topology (example: tap in the pipe run to a shower. Tap can act like a "short circuit". Star topology is better than point to point).
    Combi boiler too small
    No thermostatic mixer on the shower
    High flow rate shower installed on otherwise adequate pipes.
15. • CommentAuthorJoiner
    • CommentTimeJan 9th 2012

     
    "Poor topology (example: tap in the pipe run to a shower. Tap can act like a "short circuit". Star topology is better than point to point)."
    
    Which is why it tends to be more of a problem in older properties where a shower is a retrofit and its plumbing taken from the nearest convenient point, usually just tee'd in.
16. • CommentAuthortony
    • CommentTimeJan 9th 2012

     
    In my experience mains cold mixed with gravity hot is way and away the biggest problem area and can be sorted by putting both h & c onto gravity even without t.static shower.
    
    There are some showers expensive t. static ones that claim to work OK with a mains/gravity disparity.
17. • CommentAuthortony
    • CommentTimeJan 9th 2012

     
    They should sort your problem
18. • CommentAuthorShevek
    • CommentTimeJan 13th 2012

     
    Thanks, posted query here too:
    http://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1326031696
    
    This isn't an existing situation by the way. Just one I want to avoid.
19. • CommentAuthorandy500
    • CommentTimeJan 13th 2012

     
    Dynamic pressure vs static pressure - a lot of megaflo systems in larger houses perform miserably because the fitter didn't check the capabilities of the incoming water supply first - with everything off static pressure can be 3 bar, but when 4 taps are full on, dynamic pressure can drop to virtually nothing.
20. •  
      CommentAuthorSteamyTea
    • CommentTimeJan 14th 2012 edited

     
    What's the problem, it is all contained in this simple formula, it does not matter that it is for gas as no one is going to use it:

    
21. •  
      CommentAuthorJSHarris
    • CommentTimeJan 14th 2012

     
    <blockquote><cite>Posted By: SteamyTea</cite>What's the problem, it is all contained in this simple formula, it does not matter that it is for gas as no one is going to use it:<div id="Attachments_130037" class="Attachments"><ul><div><img alt="Plumbing.jpg" src="/forum114/extensions/InlineImages/image.php?AttachmentID=2501"></img></div></ul></div></blockquote>
    
    Perhaps worth noting that the change in static pressure at any point in a pipe network due to flow rate variation isn't connected to dynamic pressure.
    
    Dynamic pressure is the pressure associated with the velocity of the fluid flow, and as such has no real connection with the static pressure drop in pipe systems, The formula is Pd = 1/2 rho VĀ², where Pd is in Pascals, rho is fluid density in kg/cu m and V is velocity in m/S, but it's only really of use in water systems if you want to do work with the moving water (Pelton wheel, water jet, rotating garden sprinkler, hydrofoil etc).
22. • CommentAuthorCWatters
    • CommentTimeJan 14th 2012

     
    I like the water/electricity analogy. Taps and other holes in a pipe act a bit like a short circuit or high power load. They reduce the pressure (voltage) to devices down stream (particularly so if there is any resistance upstream).
    
    If Rtap is too small or Rpipe too large then turning on the tap changes the voltage/pressure at the shower..

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23. • CommentAuthorwookey
    • CommentTimeJan 15th 2012

     
    affected.
    
    (shevek, you can edit the title by going back and editing the first post. )
24. • CommentAuthorShevek
    • CommentTimeJan 15th 2012

     
    Ta.