Hot/Cold shower problem

[Stayahead]

Had a new cartridge put in last year that adjusts the hot/cold water temperature in the shower. It seemed fine for a few weeks and now when showering the water changes from hot to cold, cold to hot. Have to be very careful when standing under the shower head in case of scalding.
Visitors will now only use the bath, particularly where children are involved.
Does anyone have any suggestions as to solve this problem please.

Many thanks

[The Builder]

Sounds like it's doing the same thing again .............. is it still under guarantee?

[AlBags]

Is this a Premium brand shower? (Aqualisa .. Mira, etc)
or standard/budget?
What's the water pressure like in your area? Have you the rising mains turned down at all?

[Stayahead]

Many thanks for your answers.
To The Builder: Cartridge was installed at the same time I was having a new boiler installed, so I don't know.

To Albags: It is a quality shower, water pressure obviously varies, though I have a Power Shower, and I have never adjusted the mains pressure.

[AlBags]

If you think the HW head matches the requirements, and cold pressure is ok, there is no alternative than to replace the cartridge again.

[Stayahead]

Albags. Thanks again. Looks as if that's the route to go