Low hot water pressure

27 Mar 2005
Reaction score
United Kingdom
I have recently replaced a bath and taps. The old bath had separate hot and cold taps. The new bath has a mixer tap (that can also output mixed water to a shower head). The bath has been installed with taps at the opposite end in comparison to the old bath. The hot and cold water supply pipes have therefore been extended.

The horizontal hot water pipe (22mm) previously joined directly to the old tap using a flexible hose (22mm fitting on tap). After removing the old tap connector, I have added an isolating valve, two 90 degree bends joined by a small length of vertical pipe, an extension of approx. 650mm (horizontally), and then a 22mm to 15mm reducing connector. Finally, the tap is joined to the 15mm supply pipe using a flexible hose.
The hot water pressure is now very low. However, if I remove my new pipe work from the isolating valve, then open the valve, the pressure seems fine at that point.

I have checked for obstructions in the tap, but is seems OK.
Cold pressure from the new tap is fine.
Other hot water taps in the house are fine.
Could the 90 degree bends cause pressure loss, or the reducing connector?
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is the new tap a ceramic disc type or conventional spindle and rubber washer.

Is the hot water poor even with the cold turned off :?:

I’m not sure about the tap type.
There is a spindle coming out from the base of the tap’s spout. Part way down the spindle there is a junction (that can be rotated around the spindle). The junction has two connection inlets (one on each side), one for hot and one for cold. These hot and cold inlets are each connected to separate assemblies which are used to adjust the flows.
The very bottom of the spindle is connected to the shower head.

Hot is always poor, with or without cold.
I'm afraid a lot of these taps on the market are designed on the continent were hot water is often under high pressure. Here in the uk our 19th century low pressure hot water systems with a copper cylinder fed from a tank in the atic are of course the norm.

Result poor hot water flow.

Some of the british makes eg "Bristan" are an exception.

My advice would be to try and conect the old tap if u have it and see what that is like. If this is not possible because the new tap tail is of a smaller diameter then again the tap is the culprit.
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I've put the old tap back on and it works fine. It looks like you are correct and it is the new tap that is the cause of the problem.
Is there anything I can do to increase the hot water pressure, e.g. add a pump?

I understand pumps can be used as long as the water system is not 'unventilated'. I think my cold water is fed from a tank in the loft, but I am finding it difficult to be sure due to a complicated solar water heating system left by the previous occupants (that is not used).
There is a copper tank in the loft. It is split into two sections. The top has a lift off lid and contains cold water. It also contains a ball valve.
I cannot see inside the bottom section as it is completely sealed, but although it is lagged with insulation, it feels cold. I think the top and bottom halves are linked by internal pipes, but I am not 100% sure.
The top half of the copper tank is connected to a separate lower plastic tank. This tank has a lift off lid and contains (very dirty) cold water and another ball valve. This tank is also linked to the overflow.

My hot water is stored in a cylinder in an airing cupboard on the first floor.

I can turn off the kitchen and bathroom cold water by turning off the stop cock under the kitchen sink.

Will a pump be compatible with this system, or is there any other alternative?
I don't have the ability to add the pictures myself, so I've emailed them to admin. I don't know whether they will get posted today though, because of bank holiday in UK.
kevplumb said:
I understand pumps can be used as long as the water system is not 'unventilated'.

the opposite actually

Have you been drinking Kev? It's a double negative, and he's perfectly right. System's not unvented, ie it's vented so pump's ok.

can you post some pic's this sound's complicated :confused:

"sounds complicated'' = "hic! oops! my glass is empty again" :D
why do i bother
;) ;) ;) ;)
No problem. That was a genuine thanks....I was just off to find a pump shop. Like you say, wait for the pics to be sure. :D
grunfos do a pump for UK hot water systems but they are blloody expensive.

The cylinder in the atic sounds like whats called a combination cylinder. It's probably heated by water that circulates through the solar collectors and then through a coil type heat exchanger inside the bottom "completely sealed" bit of the cylinder, the small plastic tank with a lid will probably be part of this system.

I would be concerned were the water from your hot water cylinder on the first floor comes from. Some of the older solar (especially DIY) systems used the solar energy to preheat water before it went through a final convetional heating stage. If your hot water originates from the copper cylinder in the atic the whole thing sounds like a good breeding ground for Legionella. This can be caught very readilly by taking a shower in infected water. The resulting pneumonia carries a significant mortality rate.

If you don't have a large black plastic or large galvanised steel cold water cistern (tank) (full of water)either in the atic or in the airing cupboard then I would have the hot water system checked by a reputable solar heating consultant.
kevplumb said:
dont get your back up mate its only banter ..........

Put the bottle down, it's making you a bit over sensitive

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