Mixer tap on a gravity fed hot water system

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Mixer tap on a gravity fed hot water system

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ksareen

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Hi all

Just moved into a house and out of several things the wife complained about was that there were seperate taps for HOT and COLD in the bathroom sink. She wanted a MIXER instead and she gets what she wants.

The basin HOT water tap is gravity fed but the mixer shower valve is pump fed (negative head). The expansion tank (at the top), header tank (in the middle) and copper tank (at the bottom) are all in the first floor airing cupboard.

The issue I've now is that the HOT WATER pressure is much less compared to stand alone tap. The COLD WATER is as good as before but when used as a MIXER tap, the cold is actually pushing HOT WATER back and filling up the HEADER TANK (overflow fitted).

When installing the mixer basin valve, I used the flexi hoses with isolation valves built in. Can they reduce the flow rate?

Is there a way to fix this or should I go back to stand alone taps. I could put pressure reducing on COLD TAP but how to get the HOT WATER back to its original flow rate?

OR should I feed the HOT WATER from the pump.

The hot water flow rate in the kitchen sink (mixer tap) is also not very good. What I've also noticed is that the OLD ball valve in the header tank is slower to fill the header tank compared to the New ball valve in my cistern. Not sure if it matters though in this situation.

Thanks for yout help in advance..
 
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There is a similar thread not that further down forgot the name.

You could reduce the flow using the service valve just close it half way.

I can't remember the other solutions...
 
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Thanks mrlennie

You could control the flow, not the pressure through the service valve and it will affect all other parts of the house (including garden hose) which I don't intend to.

I can possibly control the flow through the isolating valve on the flexi tap hose, but do I need to do that?

How do I get the hot water flow rate back?
 
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Yes I meant the valve on the flexi. Try it see what happens. you need a screwdriver to do it.

How do you get the hot water pressure back? It may be low because your cold is forcing it back? Is it low all over the house? I'll just re read your post...
 
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OK, I will change the pressure setting on the flexi valve, but I doubt that will change anything.

Hot water is weak on it own, without the mixer (COLD inlet) affecting it, which is the main problem!!
 
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If it is low all over the house then it may just be where the tank is situated. You mentioned you wanted it back was it fine at one time?
 
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Yes it was fine when I had seperate HOT and COLD single taps instead of mixer tap on the sink.

However, the HOT WATER pressure is low downstairs as well in the kitchen (mixer tap again) but not as much as upstairs.

The copper tank is placed at the bottom of the first floor airing cupboard, its actually wedged between first floor and ground floor.

Could HOT WATER low pressure symptom be linked to the header tank by any chance?
 
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The pressure at the hot tap is governed by the height of the cold cistern.
If the cistern is 2m above the tap the pressure at the tap will be 0.2bar (near enough).
The pressure on a cold mains pipe ranges from around 1 bar to as high as 10 bar. (If it was running from a cistern, it would be 10m to 100m above the tap).
Your old taps were made to suit low pressure with big waterways inside. Most new mixers are only suitable for high pressure (although you can get low pressure ones) and should be supplied from balanced supplies with check valves fitted to the tails.
If, as it sounds, your cold is mains fed the tap will never work properly no matter what you do. Fitting a pressure reducer to the cold will only make the cold as bad as the hot. You need to buy a different tap or learn to live with it. (or change your system to an unvented or a combi.)
 
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Thanks tamz
The water level at the header tank when its full (ball valve closed), is about a meter higher from the basin tap, so you are probably right that here is not enough pressure for the HOT WATER TAP.

Buying a new tap won't be easy as this tap was bought specially when I was in India. I've a lovely but 2 hole basin in bathroom and I could not find any mixer taps with flexible legs for a 2 hole basin here. So I bought one when I found one in India. Due to its flexible legs, it also makes the tap outlet much higher than the previous single taps, which does not help!!

I've another option I think, I've pumped (Single negative head for HOT water only) supply for Jacuzzi, should I link the pump outlet to basin HOT WATER tap as well?
 
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Hi again

I've attached pics of my new mixer tap. I find it weird looking but missus likes it. I've also attached a pic of my airing cupboard setup.

So I am going to give it a hot water feed from the shower pump unless someone on here tells me otherwise (please let me know in time).

SOOO many thanks once again for your help.
 

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However you go about it, your pressures need to be balanced.

You might get away with installing a PRV in the cold supply to it.

Remember that to comply with water regs you need a double check valve in the cold supply too.
 
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To stop the hot water (tank fed) finding its way back down the cold pipe in the event of a break in supply.
The rules are sometimes a bit hypothetical but they have to be followed.
 
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None like that ,id just change the basin and have a nice looking mixer:cool:

The basin is nice, as long as mixer does its job, I am fine.

tamz, mrlennie, WHPES
thanks for your input and help. Could you please send me some links for PRV and double check valves. I want to make sure that I understand (sorry still a learner:)

I was thinking of installing a balancing valve with mains cold feed on the hot water supply. Wouldn't that minimise the use of mains cold tap anyway?
 
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By balancing valve I presume you mean Thermostatic Mixing Valve? Even with one of those you need to balance your supplies.

Double ckec valve available from any plumbers merchant or screwfix. PRV here Comap PRV With Gauge 15mm x 22mm - NoLinkingToThis, Where the Trade Buys.

Flow limiter is small plastic gadget available from any plumbers merchant
 
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tamz, please refer to my post before. I am going to increase the HOT WATER pressure by giving it the output from my bath's shower pump (single negative head). So I expect the HOT WATER pressure to be little more than 0.05 bar ;)
Thanks

WHPES
Thanks for the link. I like the pressure balancing valve that Tamz mentioned more than pressure reducing valve. I've fed hot and cold feeds using flexi hoses with built in isolating valves.
Looking at the pics on screwfix for double check valves, they look so similar to isolation valves, which my flexi hoses are built with anyway. In fact I am adjusting the flat screw on the iso valve on the flexi pipe to lower the mains cold pressure.

If there is a difference between iso valve and double check valve (Both seem to have directional arrows on them), please let me know.
 
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Yes, different thing totally. DC valve is a form of non-return valve. With your type of mixer tap, this is a legal requirment on the cold feed. Don't tamper with the nut on a DC valve or the thing will fall to bits!
 
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If you are going to pump the hot, the equalising valve will be fine.
A double check valve has 2 plastic seals held in position with small springs. They only allow water to pass in one direction (as shown by the arrow). The water pushes on the seal and the spring allows it to move back and let water through. If you fit it the wrong way around the water pushes the seal shut. The screw in the middle is for test purposes to confirm that it is still acting as a double check with both seals functioning as they should. A single check valve has only one seal inside and no test point. You can use 2 singles one after the other, instead of a double.
 
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WHPES, TAMZ, thanks for the load of info. You guys rock.

P.S. I think double check valves are very useful the way you describe. I am going to install them on all mixers (bath, tap and shower) on both HOT and COLD feeds.
 
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Don't do that. Completely unnecessary on the hot and the shower will already have integral ones present in the mixer. They are only to comply with the water regs in the event of a fault and do not have any usefeulness in normal operation.
 
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The reason for doing both HOT and COLD was that at the moment, when using both taps (as mixer), the cold is pushing HOT water back into the copper cylinder and into the header tank. DC valve would stop that.

But you are right. When I would install pumped HOT and equalising/ balancing valve, then I won't need DC on the HOT pipe.

Thanks once again.
 
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