Cylinder slow to refill

Discussion in 'Plumbers' Talk' started by Bust123, Feb 25, 2018.

  1. Bust123

    Bust123 New Member

    can someone please help?

    We have had a 210 litre unvented indirect cylinder installed we bought it but unfortunately we couldn’t use it as intended as we couldn’t get the required 20 litres per minute. So we are using it primarily as a vessel, we have had a tank in the loft fitted too and are due to fit a pump soon. However the tank is taking 4 and a half hours to fill. Is that right? Surely it should be quicker than that? Our plumber said it was because the tank is really big?
  2. You had an unvented cylinder fitted - only to find out your mains water supply ain't good enough to 'power' it?!

    So the solution was then to revert to a 'gravity'/vented system with a large CWS in t'loft? And this supplies the unvented cylinder which is now effectively used as a vented type?


    I'm guessing from your symptoms that the mains 'flow' at ground level seemed ok, and this led you to believe that it would be fine to power your unvented system? But you've now found out that the pressure behind this flow is pants, so ain't strong enough to 'power' the unvented.What's more, this weak pressure falls away rapidly with height, so the CWS - which is at the highest point of yer hoosie - is taking an age to refill.

    That's all guesswork, of course.

    How large is this CWS? A typical size would be around 200 litres - is yours much larger than this? Say it is 200 litres, then a normal cold mains flow of, say, 15 lpm should in theory fill this in less than 20 minutes.

    So something is amiss. Like your tank is actually threethousandsixhundred litres size. Which it obviously ain't.

    Either there is a pipework issue to this CWS, or else the mains supply is dreadful, or else your tank is as large as the loft itself.

    Anyhoo, the good news is, there may be a cracking solution. I've been looking at pressurised mains storage cylinder booster thingies recently for my bro. Provided your water authority allows it (and many/most do), then you fit this somewhere convenient in yer housie - ideally somewhere out of the way like a garage or utility room, and this boost-pumps the cold mains water and stores it at between 3 and 4.5 bar pressure in an accumulator (typical size 200 litre, tho' you can get larger and smaller). This will refill the accumulator at the max allowed rate of 12 lpm from the mains, so to refill from empty would only take just over 15 minutes - not that it should ever empty.

    You can use this to then supply your proper unvented hot cylinder at full chat, and to get rid of the CWS in the loft.

    Cost from below £1k, and an easy plumber install (apart from connecting it to your unvented cylinder which requires G3 or summat)

    Challis CB+ 240, or Stuart-Turner MBF 200 or Grundfos 3.0 Bar Home Booster Set ( )

    However, if you are happy with your current setup - CWS supplying a 'vented' cylinder, and the only issue is the time the CWS takes to refill and this is down to very poor mains pressure, then a very simple and cheap option is to fit a mains booster pump to the CWS's inlet - eg a Salamander

    BUT, I would want to know - like you - why the CWS is taking so long to refill. Your plumber's reason doesn't add up for the reasons I mentioned before.
  3. Bust123

    Bust123 New Member

    Thanks for your response. We bought the unvented cylinder as another plumber didn’t check our litres per minute and said it would be fine and we got another plumber who checked the lpm and said we couldn’t install it as we had only 13 lpm from the mains. We was going to exchange all pipework from the mains to 22mm but we found out that, in order to do that we would have to rip out or kitchen.

    So plumber said it would ok to use the unvented just as a vented (to not waste money) and put a pump on the shower (separate feed) to get a good shower and then a tank in the loft for a gravity fed system to get a good flow into sink/bath etc, Said tank in the loft is around 227 litres, it is currently full up be we are not getting any flow in relation to the hot water from the now vented cylinder in our airing cupboard..... 6 hours later. The water is being fed to the bottom of the vented cylinder and the pipe work is at the top.

    Plumber said it’s becuase of the size of the tank and we are effectively trying to get 500 litres??
  4. The Teach

    The Teach Screwfix Select

    Consider having the cold water pipe changed/upgraded to supply higher pressure and flow.

    Ok it involves spending some cash but having a decent hot/cold water system in the norm nowdays.
  5. terrymac

    terrymac Screwfix Select

    Are you saying that you are not getting any water coming out of any hot taps at all ? If the loft tank is full of water ,then you should get water coming out hot taps. It may not be hot though . so maybe its air locked or there is a closed valve .
  6. I don't quite follow - but it sounds like your plumber is talking pants.

    That 227 litre CWS in the loft - does that fill up quickly enough (say, in 20 minutes)?

    I don't know what you mean by "we are not getting any flow in relation to the hot water from the now vented cylinder in our airing cupboard..... 6 hours later." If you are saying you are not getting a HOT gravity flow out your taps, then that sounds like an airlock issue as others have said.

    Give some consideration to the Grundfos (or ST or Challis) booster system I mentioned - this WILL give you a powerful, non-pumped, flow to all your taps. And you can revert the unvented cylinder to what it actually is - unvented.
  7. The Teach

    The Teach Screwfix Select

    Really need the mains water supply upgraded to higher flow and pressure,having an unvented cylinder on a vented gravity hotwater system can only be considered temporary.

    Different parts of the Uk have different regulations :)

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