Shower is not activating hot water?

[zenonithus]

Hello all, first post here. My shower has been playing up lately. It feels like it's lost pressure and goes cold after a couple of minutes. The copper pipe for the hot water from the combi boiler is cold so it's not activating the hot water for some reason. If I run the tap that activates the hot water the shower water goes hot but it goes extremely hot, too hot to have a shower then cold again when the hot water goes off. I took out the mixer cartridge and not sure if anuything is wrong with it though not sure if I fitted the tap back on properly. Any advice would be great as to what could be the cause.

 

[Gasmk1]

Its more than likely the boiler at fault need to get it looked at

 

[zenonithus]

ok thanks Gasmk1. It's due for a service so maybe the issue can be ressolved then