Leak from bath taps diverter

Svenena

I've got a shower over the bath where the shower hose comes vertically from the middle of the taps and is controlled by a knob in front of the hose, that you pull up to divert the water from the bath taps to the shower. The problem is that when I run the taps to fill the bath, without pulling up the diverter knob, water is coming out of the actual knob area.

I've removed the knob mechanism to have a look at it. It has three rubber seals, which all look fine. Inside where the knob sits is all filled with water (even after turning off the water and emptying the taps), so I'm not sure what it is there. Water does bubble up here immediately when I turn the taps on with the knob mechanism removed, so it obviously is meant to block the water coming up when it's in place, and is failing to do so.

It seems like the issue must be that there isn't a good seal between the tap fixture and the knob mechanism, but it does look like the threads and seal are okay.

Could anything else be causing this? It seems like it must be a little thing, so I'm reluctant to immediately call for professional help when I may be able to replace a part myself. Thanks in advance for any help.

Jackmydad

What sort of seal are they? If they are o-rings, then if you examine them carefully you may well fins that they have worn "flat" on the outside. Replacements are cheap. Lubricate sparingly with either white silicon grease or a little Vaseline.
If the tap body is worn then it's a new unit I'm afraid.
I've just seen this unit linked to from elsewhere.
https://www.amazon.co.uk/dp/B00AVUQJ7M/ref=cm_sw_r_cp_tai_R3bPzbY4245HH