Hi

We have a modern house (4 years old) with an unvented HW & CH system.
A Vaillant boiler with integral circulation pump, a pressurised hot
water cylinder, a small expansion vessel above it and lots of pressure
valves!

Three seperate questions:

1) We get a lot of air in the Hot Water, in comes out the tap looking
white because it is full of tiny air bubbles. Not a major probblem in
it's self, but is it telling us something else needs fixing? Can it
be fixed?

2) Upstairs Water Pressure Issues. The upstairs mains cold water
seems to be also regulated by a pressure valve - this seems to be a 3
way preasure valve, taking mains water in and feeding (max 6 bar?)
cold water to both the ho****er cylinder and the upstairs cold taps.
The issue is that when filling the bath, if you turn both Hot & cold
taps on, the resulting pressure is substantially less than only having
hot on or only having cold on, what is going on? Why does the cold
water need regulating in the first place (just to balance it?) and is
something not working right?

3) Rads in the loft. We are having a shell loft conversion completed
and intend to extend the current CH system into the loft. Are there
any issues with having rads higher than the expansion vessel in the
closed 2.5bar ish CH system? If this does cause issues can I just
raise the pressure vessel?

Thanks in advance.
Kev

Kevin Walton wrote:

Hi

We have a modern house (4 years old) with an unvented HW & CH system.
A Vaillant boiler with integral circulation pump, a pressurised hot
water cylinder, a small expansion vessel above it and lots of pressure
valves!

Three seperate questions:

1) We get a lot of air in the Hot Water, in comes out the tap looking
white because it is full of tiny air bubbles. Not a major probblem in
it's self, but is it telling us something else needs fixing? Can it
be fixed?
Possibly by reducing the water temperature of the HW cylinder.
Otherwise probably not as it is dissolved air coming out of solution
when the temperature rises and the pressure is reduced (as it flows to
the taps). But fixing (2) would probably help a bit.



2) Upstairs Water Pressure Issues. The upstairs mains cold water
seems to be also regulated by a pressure valve - this seems to be a 3
way preasure valve, taking mains water in and feeding (max 6 bar?)
cold water to both the ho****er cylinder and the upstairs cold taps.
The issue is that when filling the bath, if you turn both Hot & cold
taps on, the resulting pressure is substantially less than only having
hot on or only having cold on, what is going on? Why does the cold
water need regulating in the first place (just to balance it?) and is
something not working right?

Yes it is to balance it. Describe how water gets from the road to this
valve.
For an unvented cylinder to work really well you need:
The effect is also probably downstairs as well but is less noticable
when running a sink rather than a bath.

Minimum 25mm Plastic water main underground.
Minimum 22mm pipework to the valve.
Also full bore lever (for main cut off).


3) Rads in the loft. We are having a shell loft conversion completed
and intend to extend the current CH system into the loft. Are there
any issues with having rads higher than the expansion vessel in the
closed 2.5bar ish CH system? If this does cause issues can I just
raise the pressure vessel?
None at all. See FAQ. 2.5 bar is too high, run the system at the right
pressure as shown in the boiler instructions.

HTH

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html

Ed Sirett wrote in message
Yes it is to balance it. Describe how water gets from the road to this
valve.
For an unvented cylinder to work really well you need:
The effect is also probably downstairs as well but is less noticable
when running a sink rather than a bath.

Minimum 25mm Plastic water main underground.
Minimum 22mm pipework to the valve.
Also full bore lever (for main cut off).



I've got an unvented hot water cylinder with the pressure reducing
valve at 1 bar and it works fine. When one tap is on and another is
opened there's sufficient flow to feed both taps.

"adder" wrote in message
m...

Ed Sirett wrote in message
Yes it is to balance it. Describe how water gets from the road to this
valve.
For an unvented cylinder to work really well you need:
The effect is also probably downstairs as well but is less noticable
when running a sink rather than a bath.

Minimum 25mm Plastic water main underground.
Minimum 22mm pipework to the valve.
Also full bore lever (for main cut off).

I've got an unvented hot water cylinder with the pressure reducing
valve at 1 bar and it works fine. When one tap is on and another is
opened there's sufficient flow to feed both taps.

A pressure reducer acts a regulator when set so low in relation to your
incoming pressure. If your mains pressure is 2.25 bar and you set the
pressure reducer to 2 bar then with a few or more taps on one may affect the
other.



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"Ed Sirett" wrote in message
...

2) Upstairs Water Pressure Issues. The upstairs mains cold water
seems to be also regulated by a pressure valve - this seems to be a 3
way preasure valve, taking mains water in and feeding (max 6 bar?)
cold water to both the ho****er cylinder and the upstairs cold taps.
The issue is that when filling the bath, if you turn both Hot & cold
taps on, the resulting pressure is substantially less than only having
hot on or only having cold on, what is going on? Why does the cold
water need regulating in the first place (just to balance it?) and is
something not working right?

Yes it is to balance it. Describe how water
gets from the road to this valve.
For an unvented cylinder to work really well you need:
The effect is also probably downstairs as well but is less noticable
when running a sink rather than a bath.

Minimum 25mm Plastic water main underground.
Minimum 22mm pipework to the valve.
Also full bore lever (for main cut off).

Many unvented cylinder have a pressure balancing valve after the pressure
reducer. I assume this has one. The cold supplied leaves this and are the
same pressure as the hot. When a kitchen tap is turned on the pressure
balancing valve ensure equal pressure on both hot and cold and prevents
scalding, or discomfort, in the shower.



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