Poor Hot Water to Shower/Bath PLEASE HELP!

[superspringer]

Hi guys, im hoping someone can help me score some serious brownie points with the mother of my new ladyfriend. THe problem goes like this: (You'll quickly pick up that I'm most definitely not a plumber so please be patient).
Her house has a hot water tank on the 1st floor. THe hot water reaches most of the house fine, with seemingly good pressure and flow. However, the bath HW tap has very poor pressure as does the shower. (Bathroom is next to the airing cupboard with HW tank in it). The shower fails to get anything over lukewarm. THe shower was installed about 6 years ago and although never wonderful, did used to get up to temperature. Running down from the ceiling above the shower are 2 pipes feeding it, the hot one gets very hot to the touch when the shower is on despite the fact that the water flowing from the shower is cool. (To me this indicates poor flow?)
In the airing cupboard are 3 taps controlling the flow of the hot water around the house, and the one on the pipe for the bath is stuck solid with the red turning handle bit lost:

My assumptions are:
The pipe that feeds the bath and shower is partially blocked. (Or having re-read the post the tap is partially closed???) I would hazard a guess that the pipe that shoots downwards is the original and feeds the bath, while the one that goes upwards is the more recent addition and feeds the shower. Does this sound like it fits convention? (Im fairly sure the join at the top of the image is a T piece rather than a 90 deg bend, although I only had a 5 minute look the other day so may be wrong....(If it is indeed a 90 then the pipes in the bathroom must tee off from the bath, run up the inside of the wall then down the outside to the shower, which seems a bit long winded).
How do I turn off the system so that I can bleed the water from the pipes and remove the valve in the picture? I would hope to find it caked in scale or something which I can clean, then bask in the glory that awaits me....
If that is fruitless then the only thing I can think of would be that both the shower mixer unit and the bath tap are a bit scaled up. Is it possible to strip a shower mixer (it has 2 knobs, one for temperature and one for flow) to clean, and if so what would you use? I had the Idea to turn off the hot water supply, drain the shower, then turn the tap on and back fill the unit with a limescale removing solution. Would this kill the internal seals? Any help/ideas would be gratefully received. Thanks in advance. Adam.
PS In return I am a turbocharger engineer so If anyone wants to know about Turbos Ill happily trade information!
PPS Just re-read again, and if the join above the questionable tap/valve is indeed a tee, then this valve will have no effect on the shower. On or off, blocked or not the shower should still work.
My head hurts.

 

[Agile]

My advice would be NOT to tamper with the mother's system but to advise her to get a competent plumber.

We read of so many DIY disasters. If you dont know what you are doing then leave it alone. Advise her to call someone.

If you mess it up then will you pay for the professional help? I would say that you would be obliged to! What about if you spill water and bring down the ceiling downstairs? You will not have insurance!

You also need to learn the difference and relationship between pressure and flow.

Tony

 

[superspringer]

Fair point and thanks for the reply, but I thought this is meant to be a DIY forum?
Obviously I have no desire to create total meltdown, but is there really NOTHING I could attempt myself?

 

[Bon]

Fair point and thanks for the reply, but I thought this is meant to be a DIY forum?
Obviously I have no desire to create total meltdown, but is there really NOTHING I could attempt myself?

As Tony says, you have to have a clear understanding of how the system works before attempting to fault find & problem solve.

The first thing to do is sketch the system out as a schematic, labelling where valves are etc... While photos are good, we can't see where everything goes!

 

[superspringer]

Whilst Im not a plumber I am an engineer of a different discipline, so I do consider myself to be not a total numpty.
But I hear what you are saying - thanks for the advice.

 

[Bon]

Sorry superspringer, I edited my post after you'd posted your reply.

Can you sketch the system out in schematic format showing where all the pipes go in/out of the cylinder and to the taps and where all valves are etc...

This will help gain an understanding of how it all works and also might high-light where your problem is.

It's well within the realms of DIY competence to fix the problem, it's diagnosing (and knowing what to do when you've got water pi$$ing everywhere) which requires the expertise!

 

[Nige F]

Indeed it`s diy-able but some diy,er has put valves on places where they shouldn`t be -and whacked a few nail-in clips over the pipes .What else have they done

 

[superspringer]

Right-e-ho that will be my mission next time I visit her then. Ill draw up everything I can see, and we can try and make some progress from there.
I completely agree by the way that it would be totally foolish to attempt some half arsed fix only to end up with a big soggy mess where the airing cupboard floor used to be! Cheers for the positive response fellas.