On Tue, 20 Mar 2007 15:37:27 -0700, Andrew wrote:

Hi all,

I have a maisonette flat, 3rd and 4th floor of 4 storey block.
Pressure is very low, sometimes not enough to produce any hot water at
all in the bathroom at peak shower time 7:30am. The shower has become
unusable.

I have a combi boiler downstairs, a 7.5Kw electric shower off the
mains upstairs (selected for its low min pressure requirement) a cold
water storage tank behind the shower (base of tank just below that of
the electric shower head) supplying bath and toilet taps + cistern.

Several people have experienced similar issues in the neighbourhood
but still no action from Thames Water. Apart from chasing TW and the
council to add a pump to the block (they are the landlord) I am
running out of ideas on how to solve this from within...

The electric shower keeps cutting out now on the thermostat as
pressure is low. The shower attachment on the hot and cold mixer of
the bath gives low flow if hot open only. As soon as the cold is
opened too, the flow drops right down.

I understand it's not possible to pump from mains. There is no hot
water storage tank. Some ideas I had:

1- add a new hot water tank upstairs and an electric thermostat on a
separate timer to have a shower hot water storage, add pump and therm
shower
2- pump from the cold water tank into the combi boiler instead of
feeding combi boiler from the mains, use existing shower attachment to
test. Add therm shower later if successful. If necessary, add another
cold tank under the existing one (there's some room where old hot
cylinder used to be)
3- replace combi with standard boiler and reinstate hot water tank
upstairs, add pump and thermostatic shower (worst case!)


With any of these pumped solutions the worry is that the tank runs
dry. The mains can be so low in pressure that it could take 1 hour to
refill the tank. I need to be able to provide a shower for up to 4
people.

I'd be grateful for any thoughts on these, or any other suggestions.
#2 is the favourite at the moment, if possible. It seems like this is
an increasingly prevalent problem in London.


Indeed it is.

#4
If the pressure is good at most times of the day but not when you need
it and you have the space then an accumulator (giant potable expansion
vessel) is T'd to the incoming main and a non-return valve is added to the
main supply upstream of the accumulator. Size the accumulator to be at
least twice the water usage during the peak period, set it's charge
presssure to the lowest pressure that still works the DHW.


There is an increasing use of potable grade negative head boost pumps,
usually coupled with a potable grade storage cistern, usually installed at
low altitude (so they have a good refill rate).

A reasonable pump will probably set you back £400+


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards