I have an en suite and main over the bath shower.  The en suite is a mira 88 
mixer shower that runs from a hot water tank on the first floor into the 
loft and down the wall.  The cold is fed from a header tank in the loft 
above the tank airing cupboard.  I have replaced the washers (which comes as 
a kit) in the mira 88 a number of times and also changed the shower head and 
hose which is fitted on a riser rail.  The pipe runs are about 4m for the 
hot from the tank and 3m for the cold. The mira is about 16 years old and 
has worked well although not up to a power shower pressure.
Problem is that I have to turn the mira control right to the left when in 
the shower to get any warmth, however if I take the shower head off the rail 
and dangle down below the unit the pressure increases and very hot water 
comes out.  I then put the shower back on the riser rail and the water 
gradually starts to cool again.  The main bathroom shower appears ok.  Do we 
think the mira is faulty although would there be a suspicion that the main 
tank is badly scaled up. Alternatively would there be an air lock in the 
system to cause the problem?
 I have been badgered by my sons to get a power shower installed on both 
showers.  I understand that this would have to be fitted on the floor of the 
airing cupboard next to the tank for this to work.  Any suggestions of a 
good make to run both showers.  What do I fit at the shower end by way of a 
control?  Basically is it straight forward to install?

Many thanks in anticipation of the groups help.

Simon

Do the pipes that emerge from their respective storage tanks (H & C) make 
their way to the shower unit downhill all the way, or is there any part of 
the pipework which rises before it then falls again? If the latter, then 
you're sure to have air trapped in the rise, hindering the flow of water.

Rob Graham

"Simon ocane"  wrote in message 
news:vvvTe.3818$QQ5.694@newsfe7-gui.ntli.net...

>I have an en suite and main over the bath shower.  The en suite is a mira 
>88 mixer shower that runs from a hot water tank on the first floor into the 
>loft and down the wall.  The cold is fed from a header tank in the loft 
>above the tank airing cupboard.  I have replaced the washers (which comes 
>as a kit) in the mira 88 a number of times and also changed the shower head 
>and hose which is fitted on a riser rail.  The pipe runs are about 4m for 
>the hot from the tank and 3m for the cold. The mira is about 16 years old 
>and has worked well although not up to a power shower pressure.
> Problem is that I have to turn the mira control right to the left when in 
> the shower to get any warmth, however if I take the shower head off the 
> rail and dangle down below the unit the pressure increases and very hot 
> water comes out.  I then put the shower back on the riser rail and the 
> water gradually starts to cool again.  The main bathroom shower appears 
> ok.  Do we think the mira is faulty although would there be a suspicion 
> that the main tank is badly scaled up. Alternatively would there be an air 
> lock in the system to cause the problem?
> I have been badgered by my sons to get a power shower installed on both 
> showers.  I understand that this would have to be fitted on the floor of 
> the airing cupboard next to the tank for this to work.  Any suggestions of 
> a good make to run both showers.  What do I fit at the shower end by way 
> of a control?  Basically is it straight forward to install?
>
> Many thanks in anticipation of the groups help.
>
> Simon
>It'll be an air lock....best thing is to take the shower head off and with 
>the pipe left to rest at it lowest in the bath turn the shower valve to 
>hottest...then allow the water to run for a few minutes at full bore. If 
>this still does not fix it allow the hot water to get cold and do the same 
>thing. Air in water is proportional to temperature and is more readily 
>removed when the water is cold.

It could also be because the temperature in the hot water tank is too hot 
which causes more air.

If you get a power shower the above problem because exaggerated and you have 
to keep the temperature lower than you are used to because the suction side 
of the pump effectively flashes the hot water off to steam, even at 60C 
water temperature. Mine has to be set about 55C otherwise this problem 
causes cavitation in the pump and loss of hot water pumping capacity.

If you fit a power shower it is best to take the outlets separately if you 
can from the respective tanks...... also for the hot water side from as near 
the hot water tank as you can otherwise again the pump inlet suction will 
suck the overflow down and suck in air again causeing cavitation. My power 
shower delivers 4 gallons a minute and can empty the hot water tank. You may 
find that this tank will need increasing in size to cope otherwise it will 
be a very swift shower. Mine lasts 5 minutes before it starts to go cold!

Thanks for your reply.  The hot rises into the loft from the airing cupboard 
tank, lays on the floor of the loft and down into the shower.  The cold tank 
in the loft is elevated by a foot and the shower cold comes out the bottom 
of that along the loft floor and down into the shower cubicle.

Regards

Simon
"Rob graham"  wrote in message 
news:dfm74s$kj6$1@nwrdmz03.dmz.ncs.ea.ibs-infra.bt.com...

> Do the pipes that emerge from their respective storage tanks (H & C) make 
> their way to the shower unit downhill all the way, or is there any part of 
> the pipework which rises before it then falls again? If the latter, then 
> you're sure to have air trapped in the rise, hindering the flow of water.
>
> Rob Graham
> 

"Simon ocane"  wrote in message 
news:WlFTe.167$yF2.132@newsfe6-win.ntli.net...

> Thanks for your reply.  The hot rises into the loft from the airing 
> cupboard tank, lays on the floor of the loft and down into the shower. 
> The cold tank in the loft is elevated by a foot and the shower cold comes 
> out the bottom of that along the loft floor and down into the shower 
> cubicle.
>


Then it's pretty certain you are getting air accumulating in the high parts 
of the pipe run. Cut the pipe at this point and insert a T-piece to accept a 
piece of vertical pipe (with a 180 degree bend at the top) that reaches 
above the water level in the feeder tank. This will let any air out. The 180 
degree bend keeps trash out.

Rob