Shower mixer taps on bath not mixing correctly

[Rollerball]

The shower mixer taps in my bath are of this type of arrangement:

http://www.victorianplumbing.co.uk/...n=googlebase&gclid=CI6RhPb6v8wCFRHhGwodc3MHEw

(although mine has a much smaller shower head and a short, stubby chrome lever to switch the water output to the taps/to the shower head).

Over the past few days I've noticed that when using the shower head the water temperature varies a lot between hot, warm, very warm, just about warm, etc).

I've never taken one of these units apart before, so what is likely to be failing?

Also, how to dismantle it? Obviously undo the large central nut, but then how is the tap/shower lever removed? Mine doesn't have a nut, but I'm assuming it pulls out when the large nut has been removed?

Thanks

 

[Burnerman]

The shower change over valve is indeed beneath that nut assembly, and when pulled out there's usually a disc with a peg on it, that turns the valve inside. Normally these are OK until the peg snaps off, and then no adjustment is possible.
However, the taps need water at equal pressure, and if you have a combi boiler the output has to be sufficient.....temperature balancing being courtesy of juggling the hot and cold taps.
So - I guess the question is, has the shower ever worked as you would like, and can you balance the water flow into the bath well enough?
John

 

[Rollerball]

Thanks for the info. Up until recently I haven't had a major problem with the water temp - it's always been a little variable during use but now it's much more pronounced (and I'm adjusting the water flow the same as I usually do - I've been doing it daily for many years).

Maybe the cold water pressure is varying slightly?

 

[Madrab]

As it's a manual mixer, as it gets older it will be more affected by wear in the taps/diverter and any pressure fluctuations in the system. Fine temp adjustment will become more difficult as the components get older.
Only 3 things that wear, if its got screw down taps then the tap washers and screw thread need serviced, if it's 1/4 turn taps (probably not) then it's the ceramic cartridges to e replaced and the diverter can wear (nothing you can really do about this).

If it's over 5 years old then does it owe you anything? It may be time to replace?

 

[Rollerball]

Thanks. It's screw down taps.

If it gets much worse I may well replace the whole thing.