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Shower pump with conventional hot water system.

Discussion in 'Plumbing and Central Heating' started by amfisted, 7 Sep 2019.

  1. amfisted

    amfisted

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    Following on from another thread.

    Best describe what we currently have. A conventional system--hot water cylinder and gravity tank in the loft. In the bathroom is a bath, taps at the outside wall end under a window, electric shower on the inside wall at the other end. The electric shower has had a minor internal fault on and off for a couple of years, and its clear that the cable may of an inadequate gauge (4mm) to enable a straight swap with a new 8.5kw shower unit, although the current unit has worked fine with that cable. So rather than pay to have the cable replaced before fitting what could be yet another inadequate shower, I'm considering a shower pump to a thermostatic shower, with the pipework to the new shower valve surface mounted so I don't have to destroy the tiled wall.

    I know there are suggestions about the minimum size of the hot water cylinder and cold water tank that would have to be taken into account, but I'm going to explain what as a layman I think I have to do to put this thing together, and I'll be asking you experts to pick it apart.

    My first thought is to take the hot and cold feeds from the bathroom tap pipework, run them under the bath and position the shower pump under the end of the bath where the shower will be. The electric supply to the pump would have to be taken from the loft because we have solid walls and floors, and without looking I think I'd be OK bringing it down the wall in conduit alongside the bath (not above it)to the floor, and then channel it behind the skirting board to the pump.

    One thing I'm not sure about is draining the hot water pipework in order to manage the fittings because there are no valves that I can find in the HW supply beyond the cylinder, but I thought I might manage that by fitting one of those screw-in washing machine valves.

    The thermostatic shower could then be fitted on the bathroom wall where the electric shower currently sits, using chrome pipework to make it look nice. Hopefully, and as long as we limit our showers to a few minutes of decent flow, we won't have problems with the tank supply.

    Whatever's wrong with the above, please tell me so I can make it right. This is almost certainly something I'm going to do.
     
    Last edited: 7 Sep 2019
  2. amfisted

    amfisted

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    Another query is about the type of pump I need.

    Looking at the ones on Toolstation, some of them pump either hot or cold supplies, some will pump both. Presumably I only need to pump the hot supply so it would be the former type.

    Most also specify "positive head" only. The cold gravity tank is in the loft and the hot water cylinder in the bathroom airing cupboard. The distance between the bottom of the cold water tank in the loft and where the shower head will be is about a metre. In our situation, would it still be practical to site a pump which specifies "positive head only" under the bath?
     
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  4. amfisted

    amfisted

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    Just been in the loft to check, and we only have a 25 gallon (120 litre) cold storage tank. So a pump fed shower with our system is probably out of the question, given that I've read some guidance suggesting that you need at least 50 gallons.

    Oh well.
     
  5. bernardgreen

    bernardgreen

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    The storage tank will start to refill as soon as a significant amount of water is taken from it.

    Depending of the flow rate from the mains into the tank and the flow rate to the shower it may be that the tank never runs out of water. The water level may drop until the float has dropped far enough down to fully open the valve.

    A level sensor could be fitted in the tank to shut OFF the pump if the tank is getting close to empty. ( or sound an alarm to tell the person in the shower to rinse and turn the shower OFF )
     
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  7. amfisted

    amfisted

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    Thanks for that.

    I took the information about needing a 50 gallon tank from the Plumbworld website, though I haven't found a similar reference anywhere else. Our hot water cylinder is the same capacity as the cold storage tank, 120 litres (25 gallons), and I've found a thermostatic shower with both temperature and flow controls. So presumably we could turn the flow down to deplete the tank more slowly and still get a better shower than we do with the electric setup.

    I don't know whether I need to connect both cold and hot to the pump, but our mains pressure is very good, so presumably I'd need to do so to balance the hot and cold supplies. Or I could fit a reducer in the cold line, perhaps.
     
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