Loss of hot water pressure after changing taps!??!

16 Oct 2005
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United Kingdom
I've just moved in to a new place, and all the taps were pretty awful, so one by one I've replaced them.

The thing is the pressure on both the hot and cold taps was always really good on the old taps, each time I've changed one the pressure on the hot tap has been reduced. :( Only on the tap I've replaced though.

Now I've modernised all the taps in the house, and replaced the seperate bath taps with a mixer with shower head, I now have poor hot water pressure on all of them! It's not dribbling, just not enough to have a good shower, or fill the bath anything like as quickly as it used to. Plus due to the U shape of the kitchen tap, the hot now kinda runs all over the sink edge, whereas the cold tap easily has enough pressure to reach the sink!

I'm not too experienced in plumbing, so I don't know if there's some vacuum created, or some obvious reason why the pressure isn't as high as it was.

Any ideas?

If it helps, the house only has water heating, there's no central heating[/code]
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If it's any help - I had a similiar problem when I replaced a kitchen mixer. The new tap I fitted had 8mm flexible tails. Cold was OK but hot was hopeless.

The cold supply is at mains pressure & worked OK. I am told that these types of taps are generally designed & are more suited for installations where the hot is also at mains pressure - this is a design common on the continent but rare in the UK.

I have since replaced the tap again with a new miker with standard 1/2 inch tap connectors & hey presto - problem solved.

Hope this helps
But all the sink taps I've fitted already have 1/2 BSP fittings (Except the bath taps that are 3/4BSP) One sink I fitted braided flexible connectors on, but another I did a straight swap and used the exsisiting plumbing entirely.

(On the bath however, the cold tap had 15mm pipe, and the hot tap had 22mm!)

No matter how I've fitted them, every tap I've fitted has low pressure on the hot water.

How can a hot water system ever have mains pressure? Anything I can do to increase my bolier's pressure?
I think you have to understand the flow of water depends not only on pressure but also on resistance. You have fitted a tap with greater resistance, maybe a smaller inside diameter or some other type of restriction.
The pressure on the other hand either comes from the mains or from a water cistern in the loft for example.
Hot water would normally be from the cistern so the higher it is the higher the pressure. If you have a combi boiler, then there is no cistern and your hot water is direct from the mains cold water and is at the same pressure.
The diameter of pipe is also related to resistance.
I have just replaced a lead mains supply (1/2 in diam. bore) with plastic pipe (3/4 in. diam. bore) and due to the reduced resistance the flow has increased.
Increasing the pressure on a combi boiler has nothing to do with the flow of either hot or cold water.
:rolleyes: :rolleyes: :rolleyes:
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are they monobloc taps as the cold mains inlet is smaller than the hot
which would cause a restriction?

are they especially for high pressure?
There definately wasn't anything in the way of paperwork for the taps, or anything that would specify what tyoe of system they are for.

I've changed nothing but the taps (and a couple of bendy connecters to join them) So it must just be the internal diameter of the taps somewhere reducing the flow.

I kinda get what you mean with the resisitance thing, but if it's only the tap that has a smaller opening, then surely there would still be tons of pressure forcing the water out?

I wonder if there's anything I can do to adjust the taps themselves????
is it a combi ?
if not.....
did you turn the hot water off with the gate valve on the cold feed to the cylinder ?
have u opened it fully ?
is it stuck half open ?
check the cistern where the bottom hole is...this pipe feeds the hot water cystern...any muck stuck in the way ?

It's not a combi. There's no central heating in the house, just an immersion water heater (economy 7 and all that!)

One of my thoughts was 'is the master tap open fully again?' but it is, and the fact that every time I'd changed a tap it was only the new tap that was affected, while the others (old, ugly ones!) kept their full strength, proves that the pressure/ amount of water leaving the boiler is the same as it ever was.

Is there any way I can modify my taps?!
It just so happens I have a spare pair of tap valves that fit bothe the bath taps and bathroom basin taps (due to a set originally arriving damaged, and spares being sent as well as replacements) is there any way I can modify these to increase the flow?


Can't see that there is, when it's open it's open I'm thinking. It's the ther part of the tap that's restricting isn't it?
I think you're on a loser ben. You would have to increase the inside diameter of the tap that is causing the resistance and I can't see how you can do that. The smallest cross sectional area would probablely be at the valve seat and you would destroy the seating, but difficult to say without seeing the tap.
How much above your bathroom hot water tap is the water cistern/tank (not the cylinder with the imersion). It is this distance that creates the pressure for your hot water, now if it could be moved to higher position then the pressure would be increased.
I have opted for a electric shower using mains pressure, because my water cistern is in the bathroom and the water level would be about 18 ins. above the shower head and the pressure would mean a dribble of water instead of a spray.
the problem is that aot of the taps are made in europe where they have high mains water pressure and not old fashioned gravity fed cold water tanks in the loft :confused:
Many thanks everyone for your responses!
Looks like I'm on the lookout for a few cheap taps that will work for me!

In the bathroom the basin tap (1/2bsp fitments from both 15mm pipes) actually has pretty good pressure on the hot, but the bath (Where the hot was actually a 22mm pipe, even though the cold was 15mm for some reason!) doesn't. Is that cos the 22mm pipe is too big? Is there anything I can fit to this pipe before the tap to increase the pressure at the tap?

I'm guessing no, as the flexible conector I fitted would have already done this?

I'm just clutching at straws now!
By the way, any taps I look at that say 'suitable for systems with a pressure of 0.5 bar or 1 bar are obviously out, but what pressure do you think I actually have on a gravity fed system from my water tank?
Well the boiler's on the same floor as the bathroom. Does the hot water come straight from there I take it?

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