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Discuss Drop in shower pressure after new cold water tank install in the Bathrooms, Showers and Wetrooms area at

  1. Venger

    Venger New Member

    We had to replace our very old, round, cold water tank this week as it had split and was leaking thru the bathroom ceiling.

    Using some rudimentary maths and some online calculators, I worked out it had a capacity of approx 80 gallons.

    Having measured it, I new it wasn't going to go thru the loft hatch (I wasn't aware that you can fold them) so when talking to the plumber who I rang to do the job he said they'd put a coffin tank up there and a 50 gallon capacity would be more than enough for our needs.

    The job was completed yesterday and all was well until I had a shower this morning and there is a noticeable drop in pressure when using the main deluge fact the pump struggled to turn at all.

    The shower is an Inta Deluge Optimo, connected to a Showermate Eco S1.5 bar, twin, positive head pump.

    The main shower head is below the level of where the cold water tank is situated in the loft (it's in the same place as the old one) but it probably isn't a full 1 metre below but it never has been and there's never been a problem before.

    Have I massively shot myself in the foot by having a coffin tank?

    I'm assuming with the round tank having 80 gallons of water essentially sitting on top of the outlet that's connected to the pipe that feeds the shower, that's gonna give a lot more pressure than having a body of water that's 30 gallons lighter, laid out across 6 feet of coffin tank with the outputs on one end?

  2. Stigster

    Stigster Plumber Top Contributor!!

    The amount of water doesn't affect the pressure but the height or "head" does. The head is measured from the waterline in the tank to the outlet, a shower head in this case. Whatever height difference between the new and old tank's waterline is the head you would have lost. If your old tank water line was 1m above the shower head you were getting 0.10 bar pressure at the shower.

    If your new tank's water line is, say, 300mm lower than the old, you are down to 0.7 bar. As an example a standard Aqua Lisa thermostatic bar mixer delivers 7 Ltr/min at 0.8 bar. As you can imagine, a small change in head can make quite a difference especially if the original installation was marginal in performance for whatever shower valve you have.
  3. Stigster

    Stigster Plumber Top Contributor!!

    A low pressure shower mixer will improve things if the head is too low for your current model. Which shower do you have installed at the moment?
  4. Best

    Best Trusted Plumber Top Contributor!!

    I posted on the other thread that to check first if any valves are not fully open, like if an old gate valve was still on the pipework, or a restrictive small bore isolating valve.
    Also some crud could be blocking shower valve.
    I had assumed the reduction in head of water wouldn't make much of a diffence.
  5. Stigster

    Stigster Plumber Top Contributor!!

    Of course my comment is not relevant if the water level has not decreased by much. I was just considering that the current shower valve might have been working OK before but if there is a small loss of head taking the pressure below the operating limits of that particular valve.

    You are right in asking OP to check valve and strainers first.
    • Like Like x 1
  6. Venger

    Venger New Member

    Hi guys, many thanks for your replies and apologies for the delay in acknowledging them as I had to go out soon after posting.

    Stigster, from what you've said it's the change in the height of the head of water that's knackered me - if I'm measuring from the surface of the water to the shower head, then with the old tank it was definitely 1m, with the new coffin tank I would say that height has halved.

    I'm so bloody furious, solve one problem, create another.

    One thing I don't understand is the outflow from the tank drops out of the loft and into the shower pump which is located on the floorboards of the bathroom below, which is obviously a massive drop, this is then pumped into the shower, isn't the purpose of the pump to blast the water into the shower, shouldn't that make the height of the head of water irrelevant?

    If we didn't have the pump I could totally understand that we're completely at the mercy of gravity but I thought the pump would overcome this?

  7. ShaunCorbs

    ShaunCorbs Trusted Plumber GSR Top Contributor!!

    Does the pump run when you turn the shower on ?

    Also have the strainers been cleaned in the inlets of the pump ?
    • Like Like x 1
  8. Venger

    Venger New Member


    It didn't at first - however, moving the selector between the hand held head and deluge head, it did finally. When I switched the deluge head off midway thru my shower and then tried to switch it back on again it wouldn't until I went through the same procedure above, moving the selector between heads.

    I've never cleaned the strainers - how would I go about that?
  9. Best

    Best Trusted Plumber Top Contributor!!

    Now that you mention you have a shower pump, it is a different issue and not the head of water problem.
    I would have all filters checked and cleaned, plus shower valve.
    Also as Shaun said, tank could run dry.
    A 50 gallon tank might be only 40 actual
  10. Stigster

    Stigster Plumber Top Contributor!!

    He still has to have enough head for the water to start flow through the pump and start it working.

    Does the pump start when you lower the shower head as low down as possible?

    edit - just read the manual and only 100mm head required to activate pump so as you were!
    Last edited: Aug 11, 2017
  11. Venger

    Venger New Member

    Hi Best, thanks for the reply.

    Are you saying that we could run a 50 gallon tank dry with day to day use?
  12. Venger

    Venger New Member

    Sorry for any confusion altho I did mention we had a pump in my initial post :)
  13. ShaunCorbs

    ShaunCorbs Trusted Plumber GSR Top Contributor!!

    Put the hand held without the head on,

    Put it onthe tray as low as it can go

    Turn it on cold first let it run for a few minutes the. Turn it off

    Then again turn it on but this time fully hot and let it run for a few minutes

    Does this fix your problem?
  14. Venger

    Venger New Member

    Hi Shaun,

    I took the hand held head off the hose and laid the hose on the tray, I ran it on full cold for 3 mins and then full hot for 3 mins - both times the pump started immediately.

    I then put the temp back to where you'd normally have it for a shower and turned on the deluge head and initially, nothing happened, the pump didn't kick in and there was nothing coming out of the head but after about 5 seconds the pump started and water appeared at the head.
  15. ShaunCorbs

    ShaunCorbs Trusted Plumber GSR Top Contributor!!

    I would say not enough water going through the pump to kick it in, easy terms two options

    One fit a negative head pump

    Two re install the tank higher same or higher than the old if you can

    These both are if there's nothing else at fault eg valve half closed etc

    To check the filters there should be some valves on the feeds to the pump (from your tank and cylinder these should be dedicated eg nothing else off them like your hot to your taps etc)

    To confirm that you've turned the right valves off open the shower with the head on the floor and give it 5mins if nothing's running after then your good

    Grab a big towel

    And undo one at a time the feeds to the pump (you might need a pair of grips / tools to undo the nut)

    You should see a mesh filter if it's got dirt clean this out most of them arnt removable (the filter)

    Then re attach the flexi and move onto the next inlet
    • Agree Agree x 1
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