More Pressure on a Vented System

Discussion in 'Plumbers' Talk' started by Simon33, Aug 29, 2015.

  1. Simon33

    Simon33 New Member

    Hi all.

    I have recently moved into a single floor flat in a 1970s block and I am looking at doing some work to improve the water pressure in bathroom and on the hot kitchen tap but would like a bit of advice.

    The existing hot water system is an indirect vented system (with heating medium from a communal boiler) fed from a cold water header tank inside the flat. As the flat is only a single floor the head provided from the tank is low and thus both the hot water pressure, and cold water service pressures are very low.

    I have had it suggested that I replace the existing vented system with a modern un-vented system, thus achieving mains pressure on both the hot and cold water services. However I am a bit hesitant to go down this route as the existing tanks (hot and cold) are in an airing cupboard in the middle of the flat and thus there is no easy way to provide an emergency vent to outside the flat (as I believe is required for an un-vented system). An alternative solution which I am considering is detailed below:
    - Retain the existing hot water cylinder and cold water header tank configuration
    - Remove the cold water service outlet from the header tank and instead feed the cold water system directly from the mains pressure feed to the header tank.
    - Install a water pump (on a pressure switch - I hear the flow based switches are not up to much) on the hot water service from the hot water cylinder, thus feeding the bathroom (incl. shower) and kitchen hot tap.

    Does have anyone have any experience with a system like this - is there anything that I am missing that obviously rules the proposed configuration out? Also would removing the cold water service from the header tank allow me to replace the existing header tank with a smaller unit?

    Thanks in advance, any help/thoughts will be greatly appreciated.

    Simon
     
  2. Dave does Gas

    Dave does Gas Screwfix Select

    Salamander whole house pump, installed one last week for a client who had mains cold and hot served by a fortic cylinder, he is now being blasted out of his shower.

    Pump will cost in the region of £350.00 but works a treat.
     
  3. Ryluer

    Ryluer Well-Known Member

    Don't those salamander pumps quite noisy? Like an angle grinder?
     
  4. Phil the Paver

    Phil the Paver Screwfix Select


    Try running water through it, works a treat.:D:D
     
  5. Hi Simon
    Just read your thread
    Two things unless you are G3 qualified you cant do an unvented install yourself
    Second my new tundish ( www.hotun.co.uk ) is designed exactly for a problem like this. As long as you have a local waste or soil pipe you can connect hotun to drain without any smells coming back up

    Hope this helps
    Regards
    Russ
     
  6. Dave does Gas

    Dave does Gas Screwfix Select

    Russ, like the look of that tundish, looks better than the fanny trap method.
     
  7. Thanks Dave
    We have a model specifically for boilers coming out in about 2/3 months time and it will be supported by a very well known manufacturer
     
  8. Walt Systems

    Walt Systems Member

    Russ, the Hottun for boilers. Does high temp plastic drain pipe need to be fitted from Hottun to drain stack? Or is it copper pipe and into a 110mm plastic drain stack?
     
  9. Walt Systems

    Walt Systems Member

    Simon33, You say a common boiler heats the hot water cylinder. Is this boiler on 24/7? If so consider installing a plate heat exchanger and get rid of the cylinder. The high pressure cold water can run through the plate heat exchanger and be instantly heated. a second plate can be fitted for the radiators. Although depending on the hot water supply from the main boiler, it may need a flow switch on the fresh water cold feed to the plate to cut out the radiators pump when DHW is called. You will save a ton of space as well. And no noisy troublesome pump.
     
  10. Walt Systems

    Walt Systems Member

    Russ this does not look like high temp plastic drain pipe.

    [​IMG]
     
  11. Hi Walt
    You are correct however, in this instance, it is attached to an under-counter unvented (15 litre). These little beauties have the PRV discharge tapped off of the cold water supply side, so any over pressure will be expected to be at nominal temps thereby waste pipework is ok for the temps expected from the PRV discharge.
    That said, even a PRV attached to the "hot side" of the pipework would only be expected to be about 80degC
    The big difference between large cylinders and small is the PRV is set at differing pressures. The T&P valve on a large cylinder is set at 6/7bar whereas these small systems its only at 3bar.
    Therefore as the pressure in the cylinder rises because of temperature (assuming that the heater element has gone doolally and open circuit) the pressure in the cylinder reaches 3 bat quite quickly and t=is then released, allowing a slug of cold water to enter, reducing its temp and pressure and the cycle repeats.
    I am sure that someone here has the knowledge to plot the temp at which the valve will open, but I think it will be about 80.
    Also, this installation was retrospective it was previously installed hard piped!!! See picture
    Finally, have you ever poured a pan or kettle of boiling water down the sink? How did the pipes fair? The cycling time of hot water discharge is likely to be quite low so I would expect that most waste pipes would cope in this situation.
    I hope that this gives a fair explanation to this installation?
    Many thanks for your input though and if you had further thoughts please feel free to let me know, I want my product to be used correctly and for the right reasons, don't want to mislead anyone.
    Regards
    Russell
     

    Attached Files:

    Walt Systems likes this.
  12. Walt Systems

    Walt Systems Member

    Thanks Russ. High temp plastic pipe I believe is push fit only. Am I right?

    I look forward to the boiler PRV version. Will all makers approve? I believe ATAG approve discharge into a HepVo trap.
     
  13. Hi Walt
    Technically speaking the HDPE (100degC rated) waste pipe (from for example MacAlpine) is a type of compression fitting.
    Our high capacity and boiler units will have 32mm dia outlets specifically sized to take HDPE pipe. This outlet will not take a standard solvent weld or pushfit fitting. It is designed like that to encourage the use of temperature suitable pipework to be run from the tundish to the soil stack or relevant waste pipe by which time the flow temp should have cooled a bit.....but that's all distance of run and location dependant so we cannot dictate what the installer will deem suitable for correct use! You can lead a horse to water and encourage him to drink but after that?
    Anyway thanks for your comments Walt and I will post in the main section when they are ready.
    Did I say that they will be manufacture supported and recommended? (I can't say at this stage who, because of our mutually signed NDA! (protects both ways))
     
    Walt Systems likes this.
  14. Plumberbish

    Plumberbish Active Member

    So Simon, are you saying you want to turn your vented copper cylinder into an unvented cylinder? If you are saying that...don't! Without a vent you potentially have a bomb on your hands, unvented cylinders have the temp and pressure relief devices to cope...a normal copper cylinder isn't made to withstand these pressures...if you do go down this route be careful ...watch unvented hot water cylinder explosions on YouTube to see why we need the relief devices
     
  15. Walt Systems

    Walt Systems Member

    Thanks Russ. I look forward to the boiler version. It is about time one of these was brought onto the market. Many blocks of flats in London have been defaced by protruding overflow and discharge pipes. They look hideous - very third world looking. There is now no need for any of them. Bit by bit they should be removed. The sooner the better.
     
  16. Walt Systems

    Walt Systems Member

    Russ, the Intergas Rapid has a combined PRV & condensation pipe. Just one connection. A HepVo trap can be fitted. Would your tun dish fit the bill? I believe they supply a 25mm flexible plastic pipe.
     

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