Baffled by pressure problem with mixer shower

[haleyr]

Me and my husband have recently moved into a new house, we were told by the old tennants that once every 6 months we would need to bleed the hot water tank due to an airlock causing the shower pressure to drop.
This was happening more frequently than described (twice a week). The cold and hot water tanks are both in the loft so the pressure to the shower should in theory be good however, when the pressure goes it turns to a trickle but surprisingly when the shower head is lowered the pressure completely drops.
As we didn't want to be climbing up into the loft twice a week we had an expansion pipe fitted but this seems to have made the problem worse, we are having to empty the air lock every other day and it's not a great deal of air coming out. The pressure in all the other taps is normal. Does anyone have any ideas what could be wrong?

 

[xr4x4]

It's the hight of the cold water tank that determines pressure.

What's the pipe layout from the bottom of the cold water tank to the bottom of the hot water tank, distances etc.

My best guess is the two tanks are the same level, or close.

 

[haleyr]

It's the hight of the cold water tank that determines pressure.

What's the pipe layout from the bottom of the cold water tank to the bottom of the hot water tank, distances etc.

My best guess is the two tanks are the same level, or close.

OK, I have some measurements - hope it helps....

From the BOTTOM of the cold water tank to the TOP of the hot water tank there is a 32cm gap.

From the BOTTOM of the cold water tank to the BOTTOM of the hot water tank there is a 120cm gap.

The pipe comes out of the cold water tank at the bottom and goes down into the bottom of the hot water tank and is about 90-100cm in length.

 

[haleyr]

Does it make a difference that the hot water is from a storage tank and not coming straight from a combi boiler?

 

[picasso]

could be the cold water tank is too small and your the mains water cant fill it fast enough, dont forget it has to supply both the hot and cold supply, try running the shower and see if the tank is emptying below the take off for the hot water cylinder or the cold feed to the shower.

 

[Whitespirit66]

Does the shower hot supply have its own dedicated flange on the hot water cylinder, or is it shared with all other hot taps?

 

[haleyr]

Does the shower hot supply have its own dedicated flange on the hot water cylinder, or is it shared with all other hot taps?

Looking at it, there is one pipe that comes out of the tank and the pipe for the shower looks as though it is spurred off fairly close to the tank with some sort of valve.

 

[Whitespirit66]

Do both of these pipes come out of the flange on the top of the hot water cylinder?

Or, does one pipe come out of the top flange, and the shower pipe is joined to it further along?

 

[haleyr]

Do both of these pipes come out of the flange on the top of the hot water cylinder?

Or, does one pipe come out of the top flange, and the shower pipe is joined to it further along?

No, could this be part of the problem?

 

[Whitespirit66]

Sorry, you have confused me by answering no to two different questions.

Do you have two pipes (pipe on the right in this pic goes to shower) joined at the top flange, like in this picture?

Untitled

• Whitespirit66
• 1 Aug 2011
• 1

 

[haleyr]

Sorry, you have confused me by answering no to two different questions.

Do you have two pipes (pipe on the right in this pic goes to shower) joined at the top flange, like in this picture?

Untitled

• Whitespirit66
• 1 Aug 2011
• 1

sorry, didn't see the second question. the pipe to the shower joins it further along

 

[haleyr]

I will take a picture of it cos it looks completely different I'll try upload it in a minute.

 

[haleyr]

It's really difficult to see what is going on but hopefully this will help

[/img]

Untitled

• haleyr
• 1 Aug 2011
• 1

Untitled

• haleyr
• 1 Aug 2011
• 1

Untitled

• haleyr
• 1 Aug 2011
• 1

Untitled

• haleyr
• 1 Aug 2011
• 1