Mixer shower headache

[Mowgli82]

Rented property has a bath/shower mixer installed from a gravity fed hot water system and the cold from the mains has been supplied via prv (presumably to try and balance the two supplies).
When tenant is using the shower it apparently becomes almost impossible to blend, tenant citing that it takes only a fractional turn of cold to turn shower temp to ice! tenant has been rather problematic and constantly complaining about multiple issues and apparently a plumber has investigated but found system to be working satisfactorily when tested.
Latest advice from tenant is now that when the shower turns to very cold, if the diverter is moved to fill the bath, the water temp is ok, but when its diverted to shower its very cold (but pressure is ok?).
Anyone got any ideas as to why this may be and suggestions what would be best route to rectify? Not sure if its an issue with the mixer taps or an inherant problem with the supplies perhaps?
thanks

 

[SimonJohns]

Fit a thermostatic mixer. Saves alot of hassle. I know you can get cheap ones now. And if it's a bar. It will be an easy change

 

[PlumbBobBob]

simon i think it's bath shower taps

 

[Mowgli82]

OK - thanks for that -found some online for about £75 so not too expensive - hopefully this will stop the tenant complaining about this particular problem now!

 

[SimonG]

Needs tanked cold water supply and not mains, even with the prv there will be disparity between the pressures.

 

[Mowgli82]

It is Steve, thanks, but from Simon's response Ive found that I can get a thermostatic bath filler with shower attachment - tbh I didnt know such a thing existed - hardly a surprise there but still, you learn something new every day! lol
I take it everyone agrees that this will be the resolution to the problem?

 

[PlumbBobBob]

make sure there's an nrv on the hot feed

 

[Mowgli82]

Ok - will that need to be a dedicated tank then I presume? What sort of capacity would be required?

 

[Mowgli82]

Nrv? Am I being really thick here? (probably)

 

[PlumbBobBob]

non return valve

 

[Billy Bob Bob]

bristan brought a bar mixer out a couple of years ago that could work off low pressure gravity hot and high pressure cold it had a built in restrictor on the cold and you would use a ballofix to throttle it down,it did work of a fashion but was always a compromise