Grohtherm 1000 shower valve low flow

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I am puzzled over the weak performance of my grohtherm 1000 shower. When all connected up I am only getting a maximum of 9 litres per minute through the showerhead at normal showering temperature, even when I bypass the economy button. However when i remove the valve and measure the flow from each of the pipes i am getting 16 l/min from the hot feed and 28 l/min from the cold. The valve specification gives 25 litres a min for a balanced pressure of 3 bar and so this is roughly what i was expecting....ie 2 to 2.5 times what I am getting. The temperature of the hot water feed feels about normal...ie very hot so i cant understand the low flow rate. Am I doing something wrong or does 9 litres a min sound about right? Regards Steve
 
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Isn't there a factory set flow limiter in the shower :idea: which you can adjust to increase the flow rate. Other than that, check for crap in the filters, kink in the shower hose.
 
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The flow limiter can be bypassed by pressing the button on the flow knob and id tried that before. Perhaps the answer lies in the flow restrictors as there are 3 of them. The first restriction is at the fibre washers at the joint with the pipework. They have a fine guaze/mesh covering the hole. I assumed the guaze acted as a filter protecting the cartridges but perhaps theyre not needed?...so maybe ill remove the inner gauze bit and just leave the fibre washer part. Secondly, I have 2 of these valves and one of them has what i presume is a restrictor in the outlet underneath the valve body. See photo.
Funnily enough Ive tried both valves and there didnt seem to be any difference between them. Thirdly, there is a small black aerator/restrictor in the base of the showerhead so maybe ill take this out too. The inlets each have non-return valves which I presume open under water pressure otherwise I cant see how any water can get through. See photo
 
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Nope...still the same. Ive taken all of the restrictors/regulator/aerators out of the system and the flow rate is exactly the same at 9 l/min. Its the same for both valves too. Ive run out of ideas now and Grohe Customer Services are very slow to get back to me as well. Can anyone recommend a bar valve with a decent flow...say 15-20 l/min?
 
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I'm having exactly the same flow issue with a GrohTherm 1000 Cosmopolitan, with similar input water pressures and resulting flow. Did you ever resolve this?
 
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