Crosswater Thermostatic shower -only able to get tepid water

The pressure was good. I removed the non return valves from the shower earlier on advice from Crosswater so the hot would not be closed but could be overpowered as you describe. There are no flexible pipes, valves or connectors in between the shower pump and the showers, though the extension on to the bath was recently added when the new shower was installed. This was via a Tee-off on the pipes going up the wall to the shower, this is however all in copper pipe to the bath diverter valve.

Not sure what else it can be as it doesn't seem to be the showers, the pump seems ok, but definitely something wrong with the balance between hot and cold, though would expect the pump to normalise that. One point that I would have liked to check was the valve on the hot from the cylinder to the pump inlet, I cannot tell how open or shut this is because it is seized up as are all the gate stop valves. If this was restricted I guess that would inhibit the amount of hot able to pass to the pump. I have no evidence that there is a problem and the expectation is it would be fully open.
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You could try fitting the n/r valve into the cold side ,may create a bit of resistance to the cold coming in ,bit of a long shot but may make a difference. Did you remove n/r valves from the aqua as well ? Gate valves are notorious for failing , I would remove it and replace with a full bore lever operated valve. If after doing the above ,you still have the same problem then I would suspect the pump. If you isolate electric to pump and just have gravity hot and cold going to cross flow , see how the valve blends to temperature .obviously the flow will be very poor ,but if it blends to the temperature that you select without the pump in the equation then this is further indication of what your problem is.
Terry, thanks for your persistent help. I did initially try moving the hot NRV only but had no effect. Based upon your assessment I agree it may be something to do with the pump. I would have swapped the pumps over but as all gate valves are sized up, I was using the isolator valve on the pump hoses which was fine for all except one on the non problematic pump which has been sheared by someone using the wrong sized screw driver previously (only just found that out!!). Not sure if there are any tricks or tips for getting a turn on and off ( had thought about screwing a small screw into broken valve the isolator as a turning handle)
Do try the shower with pump electrics off ,will tell you what you need to know and less aggro.
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are you sure that the cold water is supplied from the tank, not the incoming supply? Turn off your main stopcock for a few minutes and run the showers to make sure.
The pumped hot & cold water needs to reach the shower mixer's at balanced equal pressure's,can this be checked ?

We cant see your installation so have to assume the cold water is tank fed,the hot water is fed via an essex or surrey flange,pipework is 22mm where necessary,with as few bends as possible,no air being drawn into the pumped system,no restrictive isolation valves,no additional nrv's fitted,thermostatic mixers having initial correct set up,cylinder is reheating its contents quick enough to supply enough hot water.

A correctly fitted unvented cylinder would have been a better idea although multi pumps can work to a certain extent :idea:
Hi John, the shower pumps are fed from a tank in the loft which is in turn fed from mains.

The install has been running fine for years on the setup which is cold from tanks, hot from cylinder, 22mm pipe works etc. The only recent change was a refurb on the main bathroom and install of new Crosswater shower to replace old Aqualisa, everything was find for a couple of months after install problem has started to occur recently.

Seems to point to a pressure imbalance somewhere though.
You could drop the Aquarian of the wall and with flush through the open pipe ends. First under gravity then pumped.

Would rule out blocked pipework/reversed hot and cold.
The only recent change was a refurb on the main bathroom and install of new Crosswater shower to replace old Aqualisa, everything was find for a couple of months after install problem has started to occur recently.

Thank you for the extra information,seems a mis match of components.

:idea: get that installer back they have fecked up your already (just about working) system ,or cut your losses and fit a correctly installed unvented system.

just being truthful,if its a diy install then get an expert in. sf
Replaced monsoon pump with new one with no effect, so that rules out the pump. Already replaced the CW cartridge so rules out that.

Aqualisa works normally (with lower pressure) when pump turned off, but tepid with pump turned on.

Crosswater produces tepid water with pump turned on or off, and is much weaker flow than Aqualisa with pump turned off.

Bath runs hot / cold correctly with pump on or off.

Switched hot supply from other working showers to remove flow into pump from equation. It had no effect.

Pipe work is buried in concrete floor but is static and problem has only emerged recently, though pipe work in the barhroom was modified when new shower and bath were fitted, this featured a tee-off of the pipes feeding the shower to also feed the bath to increase pressure when filling the bath.

Am now at a total loss on what the problem could be, or what to do next to try and identify and isolate the cause.
Thanks, will try to get installer back, though he is not responsive hence trying to sort out myself. Guess I could sue him, but would rather just sort it.
Hi, have managed to solve the problem, which after swapping thermostatic cartridges, removing NRV's and . trying a new replacement pump turns out to be a simple issue of the taps on the bath. The bath is connected via a simple a tee off from the pipes feeding the new Crosswater showershower.

The bath is controlled by a manual Crosswater Kia panel three way diverter with separate hot and cold Kia panel valves. Their are no indicators of on /off on either the diverter or the hot and cold valves. For some reason these were left in the full on position with supply controlled via the diverter valve which was set to a blank connection so no water ran until you selected either the bath filler or the hand shower. The overall set-up was causing a change in the pressure with the system supplying the two showers.

When the taps were switched full off, the pressure in the system returned to normal and the two power showers are now able to run normally with hot/cold adjustmentt.

Thanks to everyone for their help and assistance on this, it was greatly appreciated.

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