O.K. so you have new and different pipework and new and different shower
cartridges so you can expect different performace from the system.
If your pump is under specified or your cartridges are for a lower flow rate
then you might not get the same flow from your power showers as you did from
However normally I would expect a better flow from a pumped shower.
Does make me wonder - if you had a shower pump AND two gravity fed showers
then did you have a third shower with a pump?
If not, what was the pump for?
Probably not the problem you seem to think it is.
Firstly, I would expect the flow to increase if the temperature was turned
down (within reason).
The limiting factor for the flow (up to the maximum flow available from the
pump) is normally the amount of hot water available to mix with cold to get
the desired temperature.
Lack of hot water (volume ot temperature) tends to slow the flow.
I think maximum flow is at whatever temperature you get when 50% of the
water is hot and 50% is cold so both sides of the pump are delivering
If the hot water is way too hot then the flow slows down again as you are
getting very little hot water through and so are maxing out on the capacity
of the cold side of the pump.
Been there and got very confused.
Tinker with the hot water temperature until the flow seems good.
Accept that a high pressure cartridge may not give the same results as a
gravity fed cartridge if you had a good head of water for the gravity feed.
Secondly, the safety lock is normally set at a very conservative
In my last house I had two power showers run off one pump and they both
worked O.K. at the same time.
To get what I would consider a reasonable temperature I had to go well past
the red button.
Same with my shower in my other house in Berkshire - combi boiler so mains
pressure to hot and cold shower inputs.
Still had to go past the red stop to get a decent temperature.
No plan survives contact with the enemy.
[Not even bunny]
Yes, there was a third, pumped shower, currently out of commission for other
Indeed, but what I think is happening is that the lower temperature of the
hot is reducing the flow of cold, reducing overall flow. I ought to do some
experiments, observing any change in flow when the temperature setting of
the shower valve is changed.
The pump is delivering much better results than the old gravity feed.
There was a brief period between the plumber's visits when a new shower was
operational before he turned down the temperature. My impression,
unscientific though it was, was that the flow was better and the temperature
control did not have to be set so high before the temperature change. I
accept that the latter doesn't really make sense if the thermostatic valve
is doing its job properly - temperature setting should be independent of
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