Cold water with low pressure

the_sphinx82

Hello, I have a weird issue with cold water in my bathroom. The hot water pressure is fine, but if I open the cold water tap the pressure is very low. This happens both in the basin (two faucets) and in the shower (one mixer). In the kitchen the cold water comes just fine.
Any idea?
Thanks 🙏

Bendy_House

More info needed - is it a combi system or a stored water type? If the later, is it vented or unvented?

I suspect it's a vented system, so there's a CWS tank in the loft, and a vented hot cylinder in a cupboard. In which case it's seems to be common to only the cold supply from the CWS, so I'd be checking that to see if there's a partly-closed or blocked valve coming from it supplying your cold taps. Ideally there will be two 22mm pipes exiting the CWS near its base, one going to the hot cylinder, and one to the cold taps.

The KITCHEN cold tap will be supplied direct from the mains, so you'd expect that to be quite powerful.

If there is a CWS in t'loft, can you prise open the lid, shine in a torch, and see what the water quality is like?

the_sphinx82

Bendy_House said:

More info needed - is it a combi system or a stored water type? If the later, is it vented or unvented?

I suspect it's a vented system, so there's a CWS tank in the loft, and a vented hot cylinder in a cupboard. In which case it's seems to be common to only the cold supply from the CWS, so I'd be checking that to see if there's a partly-closed or blocked valve coming from it supplying your cold taps. Ideally there will be two 22mm pipes exiting the CWS near its base, one going to the hot cylinder, and one to the cold taps.

The KITCHEN cold tap will be supplied direct from the mains, so you'd expect that to be quite powerful.

If there is a CWS in t'loft, can you prise open the lid, shine in a torch, and see what the water quality is like?

Hi, thanks for answering. I have a combi boiler and it's not a vented system.

FreeBear

Is this a recent problem, or has it always been like this ?

I'm inclined to think the pipe supplying the bathroom is a 15mm pipe that is restricting the water flow. If this is the case, either fit a larger pipe (22mm) or a booster pump.e.g. https://showerpowerbooster.co.uk/mixed-systems/

Bendy_House

the_sphinx82 said:

Hi, thanks for answering. I have a combi boiler and it's not a vented system.

Well, that scuppers 99% of my theory. Actually, make that 100%

If the cold kitchen is fine, and the hot bathroom is fine, then I think it's highly unlikely the problem is down to the use of 15mm pipe to the cold taps. 15mm would actually be the default size to use, and provided the mains pressure is 'fine' - and it would appear to be - 15mm should be too. (Very unlikely 22mm was used for the hot, unless old pipes from a vented system were reused.)

So, what's the cause? Dunno, but my suspicion would be that there's a cold isolating valve for the bathroom that needs checking.

Or, both the basin and bath mixer taps are having individual, coincidental, issues.

Sphinx, what type of taps, oops, faucets are they - multi-turn or quarter-turn ceramic?

TELLIT01

A combi system doesn't automatically mean that the basin and bath aren't supplied from a cold water tank in the loft and that would explain the low pressure.  The OP hasn't said if it's always been that way.  If there isn't a cold tank my bet would be on an isolating valve not being fully open too.

FreeBear

TELLIT01 said:  The OP hasn't said if it's always been that way.  If there isn't a cold tank my bet would be on an isolating valve not being fully open too.

Or a badly fitted bit of pipe with a kink/dent in it.

the_sphinx82

Bendy_House said:

the_sphinx82 said:

Hi, thanks for answering. I have a combi boiler and it's not a vented system.

Well, that scuppers 99% of my theory. Actually, make that 100%

If the cold kitchen is fine, and the hot bathroom is fine, then I think it's highly unlikely the problem is down to the use of 15mm pipe to the cold taps. 15mm would actually be the default size to use, and provided the mains pressure is 'fine' - and it would appear to be - 15mm should be too. (Very unlikely 22mm was used for the hot, unless old pipes from a vented system were reused.)

So, what's the cause? Dunno, but my suspicion would be that there's a cold isolating valve for the bathroom that needs checking.

Or, both the basin and bath mixer taps are having individual, coincidental, issues.

Sphinx, what type of taps, oops, faucets are they - multi-turn or quarter-turn ceramic?

It seems multi-turn. Thanks

the_sphinx82

FreeBear said:

Is this a recent problem, or has it always been like this ?

I'm inclined to think the pipe supplying the bathroom is a 15mm pipe that is restricting the water flow. If this is the case, either fit a larger pipe (22mm) or a booster pump.e.g. https://showerpowerbooster.co.uk/mixed-systems/

I entered the flat just one month ago and since then has always been then, but I don't know how it was before. Thanks 

GDB2222

Is there a cold water storage tank? The kitchen cold tap is always off the main, but the bathroom cold tap can be from a tank. The tank may be in your flat or it may be communal.

First thing to do is ask people in neighbouring flats.

Second, if this is a rental, is ask your landlord.

Bendy_House

the_sphinx82 said:

Bendy_House said:

the_sphinx82 said:

Hi, thanks for answering. I have a combi boiler and it's not a vented system.

Well, that scuppers 99% of my theory. Actually, make that 100%

If the cold kitchen is fine, and the hot bathroom is fine, then I think it's highly unlikely the problem is down to the use of 15mm pipe to the cold taps. 15mm would actually be the default size to use, and provided the mains pressure is 'fine' - and it would appear to be - 15mm should be too. (Very unlikely 22mm was used for the hot, unless old pipes from a vented system were reused.)

So, what's the cause? Dunno, but my suspicion would be that there's a cold isolating valve for the bathroom that needs checking.

Or, both the basin and bath mixer taps are having individual, coincidental, issues.

Sphinx, what type of taps, oops, faucets are they - multi-turn or quarter-turn ceramic?

It seems multi-turn. Thanks

And does it 'feel' good? The tap I mean. When you open it up, does it spin quite freely, just like the good 'hot' one. Or is it rough, and come to a bit of a sticky halt?

Does the flow begin quite quickly as you start to open it, increase nicely, and then - what? - you keep spinning and no more comes out?

Obviously, the fact that BOTH colds are troublesome will tend to point to a single cause, but it's important to avoid red herrings in your system.