Stains on bathroom wall panels

PunkRoquefort

I have a house I am getting ready to re-let.

The previous tenant looked after the house well and left it tidy, but I have since noticed these orangey, spots stains in many areas of the panelling over the bath, toilet and basin. 

I initially thought elbow grease and a good cleaner would remove the stains.

Some areas are not stained. Those that are, you can feel on the surface.

Any ideas as to what the cause may be or remedy?

I have tried Cif, vinegar, Cillit Bang, Killrock, along with various scrubbers and scourers.

Any advice would be appreciated.

My plumber has no idea what it is or how to treat it and I am potentially looking at a very pricey replacement.

Thank you.

Working_Mum

Could be something like bleach which has been splashed on the surface and reacted?? Bleach often leaves orange spots on towels etc

I can't see anything too clearly from your pic - is it a natural stone or a fibre-board / laminate of some sort??

PunkRoquefort

It is the smooth plastic style board, which is popular these days.

It has been in there for several years. I have the same panelling in my own house, where I live, put in at the same time, but at home, do not have this issue.

grumpy_codger

Working_Mum said:

Could be something like bleach which has been splashed on the surface and reacted?? Bleach often leaves orange spots on towels etc

Bleach is unlikely to make plastic yellow, but can discolour other contaminations - it's worth trying. 
However, my usual advice is to make sure that bleach contains 'bleaching agent(s)'. E.g. this one from Tesco doesn't -  Tesco Thick Bleach 24Hr Citrus 750Ml

Rusty190

A quick Google suggests the culprit could be Magnesuim and Iron residue in hard water - don't know if you are in a hard water area?
Treatment suggested, other than what you've already tried, is make a paste using bicarbonate of soda and white vinegar.
Apply to the affected area (would suggest trial on an inconspicuous bit first) and leave for 15 mins or so to dry.
Then rinse off with warm water and dry.
Good luck.

Grenage

My first guess would be staining of limescale deposits.  Something like Viakal left to soak might work.

twopenny

You could try Milton that is used for babies bottles etc.
I spilled some on my tarmac drive and it left a clear trail.
I used it to deal with the water works in a house that had been uninhabited for some time 
.