Recently (last 2 weeks) replaced Aqualisa thermostatic Valve with Crosswater BP1000RC dual control thermostatic valve. Since new valve fitted water pressure rate very poor when temp set ok for shower (2/3 litres per minute max!)..
When thermostat set at fully cold, flow rate quite good, as soon as temp control moved to warmer setting rate of flow falls off dramatically. (Thermostat setting from factory 42 degrees -have adjusted up and down with no improvement to flow problem).
Advised that temp of hot water to valve correct at approx 60 degrees. Pump equalising pressure to both sides of valve. Have also noticed that as the hot water cools down naturally in cylinder the flow rate at an acceptable shower temp starts to improve (thermostat?). Have replaced theromstat 3 times in last 10 days - still no improvement in problem.
Gravity fed system (fed from cold water header tank and hot water cylinder) 2 bar aqualisa pump (checked for air locks and ok).
Crosswater valve has a non return valve on hot and cold input side (am told there to prevent cross flow of water).
Only pipework replaced was short (1 metre) of hot and cold input to new valve. No change to set up otherwise..other than new, larger shower head.
Sorry for lengthy query, but wanted to submit as much detail as possible. To date my plumber is unsure of how to resolve this problem. Would very much appreciate and suggestions.
I have removed the flow restrictor from the shower head. Crossflow confirm that there are no flow restrictors in main valve (see later note on non return valves)..
In addition, the main valve has a non-return valve in both the hot and cold inlets (I understand to avoid crossflow), and as as recommended by the manufacturer have removed the non return valve on the hot side only with a mariginal improvement (still only 5 litres per min when set at a comfortable showering temp).
The hot side non return valve was removed as the flow of water from the cold side was good (15 litres per min) but mixed rate of flow becomes very poor when seeking a suitable showering temp.
The output of water at the pump point ( in loft area) has been checked and is 15 litres per min on both hot and cold side..
Manufacturer has provided a new replacement valve but I am not confident that a straight replacement would resolve the problem. Maybe a different manufacurer valve?
I am not sure if this model of shower has filters fitted. If it does then of course the problem may lie there.
Measuring the free flow rates doesn't necessarily help identify the problem here.
The mixer valve may only be suitable for a high pressure system which if it was connected to the mains it would be operating at somewhere over three bar. Now if the pump you are using is only a basic model it may only be able to achieve up to 1.5 bar max which realistically is only just over the 1 bar minimum the shower needs to work.
Maybe you should consider upgrading the pump to a better model?
I have removed the filter from the hot inlet within the shower valve with no improvement to the flow.
I am advised from the manufacturer that the valve is designed to work with a low pressure system and should operate satisfactorily between 0.5 and five bar.
Following your latest thoughts I will investigate looking at a higher performance pump even though Aqualisa (current pump manufacturer) state that my existing one (2 bar) should provide sufficient volume of water to produce approx 15 litres per min at shower head at suitable temperature (currently 5 litres per min).