Non-functioning thermostatic valve

[petey]

I have a thermostatic shower valve that is just not behaving. The bathroom is an in annex and CW is supplied from a separate connection to the CWC located directly above – with a 1.8m head above the outlet. Unfortunately, the HW comes from the household supply, albeit from a new, larger cylinder with the takeoff from the side 'shower' boss. I reckon the length is c13mt in total to the new bathroom and the head is about 1.2mt. All pipework is 22mm speedifit.
When commissioned, the flow would last maybe 5 mins and then peter out.
My first step was to 'improve' the HW flow – so I installed a Grundfos UPA1590 booster adjacent to the HWC.
The result was underwhelming with a flow that lasted all of 30 secs!
My sense is that the increased HW pressure (c 0.5 bar) is way too much for the valve.
So, my little chums, any ideas/suggestions for a solution?
I am considering:
a) a booster on the CW, but this would be a problem, as the only location is below the CWC with a head of 1.2m max. or
b) a pair of regular, single end shower pumps, eg ESP 80 CPV.
Any other insight/input would be much appreciated.

 

[cross thread]

may be the thermostat cartridge thats faulty,try running it with no hot water in the cylinder to test the stat, put the valve on hot setting.it may be the valve is shutting down

 

[petey]

thanks for your input - I'll try that, tho' sceptical cos it's a brand new valve, but I see your logic. my gut tells me that it's a mismatch between the pressures, I would like some input as to yay or nay and what I can do about it.