Very low shower pressure

[context]

What I've got:

-I live in a block of flats (one level, no lofts or upstairs)
-Unvented system with a hot water tank on the kitchen wall
the top of the tank is about 2m high from the floor level.
- Water pressure cold/hot is reasonable (though not spectacular) throughout including the bath tub.
The bath is filled reasonably fast.

-I have replaced two separate bath tub valves with a mixer shower
(flexible shower hose + head) picture1
When I lift the hose to about 1.5 m higher that the tub ... no water pressure even with the head
unscrewed .
Tested with the cheap plastic mixer shower ( picture 2) instead of the metal one ... same result.

What can be the problem ?

Picture 1


Picture 2

 

[JohnD]

-Invented system with a hot water tank on the kitchen wall

Do you mean cylinder? What colour? Show us a picture.

 

[context]

Yes, I meant a cylinder, though it's enclosed in a white square wall mounted steel box
The make is
Harton CCHT Type C, Flat back J141

sorry can't submit a picture as I don't live there ( tenant does)

 

[context]

The boiler installed , if that matters
is
Vokera Mynute HE
http://www.vokera.co.uk/wp-content/uploads/2009/04/mynute-he-installation-and-servicing-manual.pdf

 

[JohnD]

Please show me the one you mean

http://hartons.co.uk/

I suspect it is open-vented, which would give the results you describe.

 

[context]

Unfortunately it's not on their site probably because it's about 15 years old, and it says 'special order' on the sticker sheet.
There is also an electrical immersion heater in this cylinder.

 

[JohnD]

I suspect it is open-vented, which would give the results you describe.

 

[context]

Thanks John, but how do I establish for sure what type it is?
I'm an electrician and have only a basic knowledge about heating systems.
I've done some research and reading/videos lately so I know the difference between the different types of systems,
but because the cylinder (tank? ) is fully enclosed I can only open a side panel and see 6 pipes:
drain,overflow, CW feed , HW output, and indirect heating input/output.
Of course I could call a plumber, but it's a bit embarrassing as I thought I could find a solution myself.
May be I'm wrong.((

 

[JohnD]

you could email those ref no.s to the maker and ask them.

The casing might come off. Take some pics when you can. See if the top lifts off.

Turn off the stopcock on the incoming watermain. Do the taps still run? If so they are fed from a storage tank, probably in the top half of that casing.

The kitchen cold tap is (almost) certainly straight off the main. Put your thumb over the spout. Try to stop the flow. Next try it with the other taps (practice in your own house and you will see the difference)

If you want a shower, you could fit a shower pump, perhaps in the gap under the bath.

 

[context]

Thanks again, I'll follow your recommendations and let you know the results.

 

[context]

Spoke to the tank maker (Harton) this morning.
They confirmed that it is an open-vented system which incorporates a hot water tank inside the enclosure.
So John was absolutely correct.

That creates a couple of new questions

If I want to install a buster pump... should it be a positive head or universal/negative head type ?
Should I use a double pump or can I get away with a single pump for hot water only?
What are the advantages/disadvantages ?

 

[JohnD]

Do the thumb test on hot and cold bathtaps.