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Discuss What is the water system from 2 sources in the Plumbing Forum | Plumbing Advice area at PlumbersForums.net

Messages
165
Hi everyone,

Just discovered that my flat has a water tank in the attic which feeds the hot water into the building and the cold water is mains fed. My question is what kind of system do I then have when hot and cold are coming from different sources?

I turned all the stop cocks off (3) in the flat and all the cold water outlets had no water, however the hot water was still able to run despite this.

Also does this affect the type of taps I have or combi boiler? Just want to make sure that everything is the way it is supposed to be for example the flat has high pressure water and I then should have the right pressure taps, any info would be great thank you.
 

Ric2013

Plumber
Messages
2,672
It's a mains (high) pressure cold, gravity (low) pressure hot system. Known, sometimes, as unbalanced pressures.

You probably have a traditional vented hot water cylinder.

If you must have mixers, go for biflow mixers that have two separate waterways inside rather than in-body mixing. If you use taps that have in-body mixing, then you legally need check valves and these will RUIN your hot water pressure. There have been several people on this forum recently who have fitted unsuitable taps and have come on here looking for advice, so it is refreshing to see someone asking the question before buying the wrong thing. Well done!

If you go for ceramic disc taps i.e. quarter turn mechanisms, or lever taps, you may be disappointed with flow: traditional taps that use rubber washers (old BS5412 and BS1010) will give better flows.

In any case, you'll need low pressure taps: low pressure being 0.1bar. You may have enough head for 0.2-0.3 bar taps if you are a long way below the attic, but not if you want very good flow rates.

An alternative would be to pump your hot water and this then opens up your tap choices to include high pressure mixers.
 
Messages
165
Thank you so much for the informative reply, I have some follow up questions with pictures as this is a great learning curve for me.

I live on the top floor and the attic is above my flat which contains the water tanks that supply the building with hot water.

How do I know what bar the pressure is? is it the dial on the gas combi boiler as it reads 1.1?

Does the kitchen single lever tap look okay (the box said suitable for gravity systems min 0.5 bar) The hot water pipe under the sink has a single check valve.

The basin single lever tap (suitable for 0.5 minimum 1 bar) (no check valves on copper pipes)

The bathtub tap is a mixer tap (no check valves on the copper pipes)

The water flow in all taps work fine, although now I understand why the cold water has so much more pressure than the hot.


Any information on the world of taps would be great thanks.
 

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Ric2013

Plumber
Messages
2,672
At a rough estimate, your hot water pressure in bar will be a little less than the calculation:

height from the cistern in loft to the tap itself in metres divided by 10

EXAMPLE: if you have 2m height, then your pressure will be a little under 0.2 bar.

If you are happy with the flow you are getting, the fact that your pressure may be lower than the tap rating of 0.5 bar doesn't really matter.

The sink and basin taps do not appear to be biflow taps, but I'm not sure about the bath.
 
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Messages
165
Thank you for the information.
I filled a 10 litre bucket in a minute so is that the equal to 1 bar in pressure?

Do you also need to be conscious of the type of shower you install for example I have a thermostatic mixer shower fitted, are there high pressure or low pressure showers just like taps?
 

Riley

S. Mod
Plumber
Gas Engineer
Messages
10,714
No flow and pressure are different. Does beg the question though why if you’ve got a combi boiler does it not supply hot water to the flat?
 
Messages
165
Well that's what I was confused about, I have a gas combi boiler, the cold is mains fed and when all stopcocks are turned off only the cold water is off but the hot water still runs.

A workman was in the attic and I asked him if their were water tanks in the attic and he said their was which then got me thinking is the hot supplied from the tanks and not mains fed?

There are no water tanks or anything which holds water in the flat but I believe since it is circa 1960s their was a hot water cylinder installed which is now an empty cupboard.
 

Ric2013

Plumber
Messages
2,672
Thank you for the information.
I filled a 10 litre bucket in a minute so is that the equal to 1 bar in pressure?

Do you also need to be conscious of the type of shower you install for example I have a thermostatic mixer shower fitted, are there high pressure or low pressure showers just like taps?
No. Please see my above post.

You'd need a thermostatic shower that will accept unbalanced pressures. Some do, but very few showers are actually designed to work well in this condition.
Well that's what I was confused about, I have a gas combi boiler, the cold is mains fed and when all stopcocks are turned off only the cold water is off but the hot water still runs.
A workman was in the attic and I asked him if their were water tanks in the attic and he said their was which then got me thinking is the hot supplied from the tanks and not mains fed.
Can you post a picture of your boiler and the hot water cylinder in your airing cupboard please?
 
Messages
165
Pictures of the Easi Heat plus combi boiler in the kitchen above the sink on wall and their is no cylinder anymore and the previous owner who was here for 8 years also didn't have a cylinder but a combi boiler, thanks.
 

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Ric2013

Plumber
Messages
2,672
Something doesn't add up then. It's unlikely to be gravity if a combi boiler is installed, and lack of a cylinder blows the gravity idea out of the water.
I don't think you're going to get to the bottom of this over the net, sadly.
 

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