shower water running hot and cold issue, while basin is fine

hello,
I got a shower water is running hot and cold issue.
I have a Vaillant boiler and have just changed a new shower problem is still present. The water in basin and kinchen is OK. Only when I use the shower it runs hot and cold. My water pressure is good. No other appliances or taps were being used while showering.
If its boiler problem, it should affect basin and kichen water as well, but why this only happens on shower even I have changed a new one?

anyone got ideas? thanks!

check shower is piped right cold to cold hot to hot that would give them symptoms if not check cartridge for muck

diverdee said:

check shower is piped right cold to cold hot to hot that would give them symptoms if not check cartridge for muck

Click to expand...

Pipe is connected ok, before it was working fine...suspecting its scaled in heater exchanger!? the thermistor is not good and more..?

Also check any in-line filters.