We have recently moved in to a 1930s house and are renovating the downstairs. We have just installed a large boiler and hot water tank. The bath has 2 separate taps (faucets) and both have about 18L/min of flow.

The shower in the same room only has 11L/min (measured by unscrewing the main shower head) regardless of temperature (and the same for the identical shower in the en-suite next door). Both have 2 shower heads (one fixed and one hand held) and when I switch on both at the same time I don't see a noticeable drop in pressure and perhaps get 14L a minute which to me implies the shower's mixer is to blame.

The shower is a Crosswater DL2000RC. My theory was that someone had reduced the pressure to accommodate two showers on the old boiler but I no longer have such a constraint.

I have tried loosening the red screws a bit which didn't seem to make a difference. Should it? What do they do? how far can I unscrew them? do they stop or do they completely come loose?

I note that the dials to enable each shower theoretically have pressure adjustment in normal operation via twisting them, however turning my handles has limited effect either way.

Any other ideas?

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  • Open up the things you marked with a red dot in your image and check if the filter is dirty. Be sure and lightly grease the seals with silicone grease when you put it back.
    – Ariel
    Commented Dec 7, 2023 at 9:35

1 Answer 1


There is a flow limiter in the head of the shower units. I suggest removing the head and testing the flow. If it improves then you know it is the shower head rate limiter.

I don't know that opening the integral shutoff at the shower valve will actually improve flow (possibly if it was used to restrict flow).

  • 2
    I have updated my question to clarify that the measurement was taken without the shower head. Any other ideas?
    – Joe
    Commented Nov 7, 2023 at 7:35

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