walk-in bath - shower attachment runs cold

[ianvs]

I have an elderly friend with a 10 year old walk-in bath. Was professionally installed but company now gone bust. Has all worked 100% for 10 years.
Hot water is from hot water tank (temp is fine) Hot and cold are pumped and the bath fills quickly from a mixer tap with shower attachment. (Two separate taps and knob that pulls up to turn on the shower attachment.)

Problem: bath fills fine from hot tap with plenty pressure and temperature but when the knob is pulled up it flows at much lower temperature (pressure is good) through the hand held shower attachment.
I assume that there must be some valve somewhere or thermostat to ensure the water does not scald but as it is all enclosed within the bath unit I cannot see how it works.
Anyone know how these work?
My guess is that the shower part is increasing the pressure and the hot cannot deliver. (failing pump?)
Has been fine for 10 years.

 

[TicklyT]

If it is a thermostatic bath filler / shower valve, they can get jammed up with limescale. Swinging the temperature control from it's hottest to coldest settings about half a dozen times with the shower running may be enough to free up the valve.

Some shower valve makers recommend doing that monthly or quarterly as 'routine maintenance' - easy enough to do as part of a cleaning routine.

Sometimes just a bit of limescale building up in the shower head can cause the temperature control to behave unpredictably.

 

[ianvs]

There is no visible temperature control apart from the taps.
I have removed the knob assembly from the mixer taps and cleaned and greased it as it was very stiff. Otherwise there is nothing visible.
This the tap assembly -

Untitled

• ianvs
• 6 Jan 2011
• 1

This is the knob assembly

Untitled

• ianvs
• 6 Jan 2011
• 1