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Johan
 
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Default mains water pressure and boiler


Hi,

Not a regular poster, but often read this newsgroup.

I have just replaced some of my cold water plumbing, and now seem to
have a problem with the combi boiler: whenever I close a cold water tap,
the boiler sounds for a few seconds as if it is about to turn itself on.
This also happens when a toilet has been flushed, and the water flow
stops. The boiler is on the first connection to the mains water. The
mains pressure is fairly high (lead pipe from the street to the house
replaced last summer). I cannot think what I have changed that caused
the boiler to do this. I used speedfit pipe and fittings (yes, I have
read lots about those on this newsgroup; I find them very easy to use).

I was old a 'hammer arrestor' would solve my problem, but this has not
worked (the one I got is made by Sioux and on the packaging it states it
will keep the pressure below 10 bar; seems a bit high to me).

Is it possible that cold water is forced into the boiler when I close a
tap, which makes the boiler 'think' a hot tap has been opened? At what
pressure would this happen?

Any suggestions on how to fix this problem?

Many thanks in advance,

Johan
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Doctor Evil
 
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Default


"Johan" wrote in message
...

Hi,

Not a regular poster, but often read this newsgroup.

I have just replaced some of my cold water plumbing, and now seem to
have a problem with the combi boiler: whenever I close a cold water tap,
the boiler sounds for a few seconds as if it is about to turn itself on.
This also happens when a toilet has been flushed, and the water flow
stops. The boiler is on the first connection to the mains water. The
mains pressure is fairly high (lead pipe from the street to the house
replaced last summer). I cannot think what I have changed that caused
the boiler to do this. I used speedfit pipe and fittings (yes, I have
read lots about those on this newsgroup; I find them very easy to use).

I was old a 'hammer arrestor' would solve my problem, but this has not
worked (the one I got is made by Sioux and on the packaging it states it
will keep the pressure below 10 bar; seems a bit high to me).

Is it possible that cold water is forced into the boiler when I close a
tap, which makes the boiler 'think' a hot tap has been opened? At what
pressure would this happen?

Any suggestions on how to fix this problem?

Many thanks in advance,

Johan


It could be that through the combi when a tap is opened the pressure becomes
negative in relation to the rest of the cold water pipework. When you close
the tap the pressure increases in the pipework and moves across the combi
and activates the flow switch, or the 3-way valve. What make of combi, they
don't all work the same way?

You could

1. Insert a none return valve just before the combi. Then this will not
allow pressure to lower inside the combi and hot water pipework.

2. Take the combi cold feed right back to the stop cock, making this supply
dedicated to the combi only. Have the cold water taps tee off this pipe at
the stop cock.

Try No. 1 first.



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Johan
 
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The boiler is a Vokera Linea. Is there any point in putting a non return
valve in the hot water pipe after the boiler, as well as in the cold
water feed to the boiler?

Johan

Doctor Evil wrote:

snip


It could be that through the combi when a tap is opened the pressure becomes
negative in relation to the rest of the cold water pipework. When you close
the tap the pressure increases in the pipework and moves across the combi
and activates the flow switch, or the 3-way valve. What make of combi, they
don't all work the same way?

You could

1. Insert a none return valve just before the combi. Then this will not
allow pressure to lower inside the combi and hot water pipework.

2. Take the combi cold feed right back to the stop cock, making this supply
dedicated to the combi only. Have the cold water taps tee off this pipe at
the stop cock.

Try No. 1 first.



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John Stumbles
 
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Default

Johan wrote:
Doctor Evil wrote:

snip


It could be that through the combi when a tap is opened the pressure
becomes
negative in relation to the rest of the cold water pipework. When you
close
the tap the pressure increases in the pipework and moves across the combi
and activates the flow switch, or the 3-way valve. What make of
combi, they
don't all work the same way?

You could

1. Insert a none return valve just before the combi. Then this will not
allow pressure to lower inside the combi and hot water pipework.



The boiler is a Vokera Linea.


I'm not familiar with this model but if it's a type that doesn't have a
diverter valve then you absolutely must NOT put a non-return valve in
the supply side (from the mains): it should say this in the manual.
  #5   Report Post  
Johan
 
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Default

John Stumbles wrote:

Johan wrote:

Doctor Evil wrote:

snip


It could be that through the combi when a tap is opened the pressure
becomes
negative in relation to the rest of the cold water pipework. When
you close
the tap the pressure increases in the pipework and moves across the
combi
and activates the flow switch, or the 3-way valve. What make of
combi, they
don't all work the same way?

You could

1. Insert a none return valve just before the combi. Then this will not
allow pressure to lower inside the combi and hot water pipework.




The boiler is a Vokera Linea.


I'm not familiar with this model but if it's a type that doesn't have a
diverter valve then you absolutely must NOT put a non-return valve in
the supply side (from the mains): it should say this in the manual.


The manual says there is a diverter valve, but this appears to direct
the water either through the central heating, or through the Domestic
heat exchanger (to produce hot water). How does this affect putting a
non-return valve in the hot water pipe after the boiler?
It does not say anywhere in the manual that a non-return valve should
not be used in the water supply, it also doesn't say that it is ok.....
Sorry to keep asking questions, but I'd really like to understand this
problem now.

Johan


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Doctor Evil
 
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"John Stumbles" wrote in message
...
Johan wrote:
Doctor Evil wrote:

snip


It could be that through the combi when a tap is opened the pressure
becomes
negative in relation to the rest of the cold water pipework. When you
close
the tap the pressure increases in the pipework and moves across the

combi
and activates the flow switch, or the 3-way valve. What make of
combi, they
don't all work the same way?

You could

1. Insert a none return valve just before the combi. Then this will

not
allow pressure to lower inside the combi and hot water pipework.



The boiler is a Vokera Linea.


I'm not familiar with this model but if it's a type that doesn't have a
diverter valve then you absolutely must NOT put a non-return valve in
the supply side (from the mains): it should say this in the manual.


I'm pretty sure it has a 3-way valve and a flow switch, hence the
momentarily turning on of the fan. Then you can. I would check with makers
first though. When the DHW is heated via the main gas heat exchanger (no
3-way valve) it uses the cold supply as an expansion route. Using a plate
heat exchanger the temperatures will get nowhere near as hot. I would put a
shock arrestor on the hot draw-off side as well. As near to any lever tap as
possible, as these can cause clunks when turned off, and the arrestor will
absorb any expansion from the combi too.



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Doctor Evil
 
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"Johan" wrote in message
...
John Stumbles wrote:

Johan wrote:

Doctor Evil wrote:

snip


It could be that through the combi when a tap is opened the pressure
becomes
negative in relation to the rest of the cold water pipework. When
you close
the tap the pressure increases in the pipework and moves across the
combi
and activates the flow switch, or the 3-way valve. What make of
combi, they
don't all work the same way?

You could

1. Insert a none return valve just before the combi. Then this will

not
allow pressure to lower inside the combi and hot water pipework.




The boiler is a Vokera Linea.


I'm not familiar with this model but if it's a type that doesn't have a
diverter valve then you absolutely must NOT put a non-return valve in
the supply side (from the mains): it should say this in the manual.


The manual says there is a diverter valve, but this appears to direct
the water either through the central heating, or through the Domestic
heat exchanger (to produce hot water). How does this affect putting a
non-return valve in the hot water pipe after the boiler?
It does not say anywhere in the manual that a non-return valve should
not be used in the water supply, it also doesn't say that it is ok.....
Sorry to keep asking questions, but I'd really like to understand this
problem now.


Johan,

No problem, you can put one on. See my other post.


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Pete C
 
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On Tue, 22 Mar 2005 21:46:16 +0000, Johan wrote:


Hi,

Not a regular poster, but often read this newsgroup.

I have just replaced some of my cold water plumbing, and now seem to
have a problem with the combi boiler: whenever I close a cold water tap,
the boiler sounds for a few seconds as if it is about to turn itself on.
This also happens when a toilet has been flushed, and the water flow
stops. The boiler is on the first connection to the mains water. The
mains pressure is fairly high (lead pipe from the street to the house
replaced last summer). I cannot think what I have changed that caused
the boiler to do this. I used speedfit pipe and fittings (yes, I have
read lots about those on this newsgroup; I find them very easy to use).

I was old a 'hammer arrestor' would solve my problem, but this has not
worked (the one I got is made by Sioux and on the packaging it states it
will keep the pressure below 10 bar; seems a bit high to me).

Is it possible that cold water is forced into the boiler when I close a
tap, which makes the boiler 'think' a hot tap has been opened? At what
pressure would this happen?

Any suggestions on how to fix this problem?

Many thanks in advance,

Hi,

Sounds like an airlock in the HW pipe after the boiler, the air will
expand and then compress as a cold tap is opened and closed due to
fluctuation in water pressure, making water flow momentarily in the HW
pipe and causing the boiler's flow switch to operate.

cheers,
Pete.
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Ed Sirett
 
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On Tue, 22 Mar 2005 23:18:05 +0000, Johan wrote:

John Stumbles wrote:

Johan wrote:

Doctor Evil wrote:

snip


It could be that through the combi when a tap is opened the pressure
becomes
negative in relation to the rest of the cold water pipework. When
you close
the tap the pressure increases in the pipework and moves across the
combi
and activates the flow switch, or the 3-way valve. What make of
combi, they
don't all work the same way?

You could

1. Insert a none return valve just before the combi. Then this will not
allow pressure to lower inside the combi and hot water pipework.




The boiler is a Vokera Linea.


I'm not familiar with this model but if it's a type that doesn't have a
diverter valve then you absolutely must NOT put a non-return valve in
the supply side (from the mains): it should say this in the manual.


The manual says there is a diverter valve, but this appears to direct
the water either through the central heating, or through the Domestic
heat exchanger (to produce hot water). How does this affect putting a
non-return valve in the hot water pipe after the boiler?
It does not say anywhere in the manual that a non-return valve should
not be used in the water supply, it also doesn't say that it is ok.....
Sorry to keep asking questions, but I'd really like to understand this
problem now.

When you had the cold water off air may have got into the Hot pipework.
If you have a 'dead' branch somewhere this could harbour some air. The
effect of the air would be for a small flow to occur through the boiler
when the cold taps are worked.

This boiler is able to dump residual heat after doing HW into the CH
pipework so this does not precluded the fitting of a non-return valve (NRV).

However since this boiler did work correctly before searching for the
trapped air is likely to be more fruitful. A NRV would solve problems. A
shock arrestor won't help IMHO.

Some boilers (e.g Ferolli) a NRV would be bad news, and the manual will
forbid it. Since residual heat would lead to expansion of the water in the
HW pipes with nowhere to go.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://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


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Johan
 
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Ed Sirett wrote:

snip


When you had the cold water off air may have got into the Hot pipework.
If you have a 'dead' branch somewhere this could harbour some air. The
effect of the air would be for a small flow to occur through the boiler
when the cold taps are worked.

This boiler is able to dump residual heat after doing HW into the CH
pipework so this does not precluded the fitting of a non-return valve (NRV).

However since this boiler did work correctly before searching for the
trapped air is likely to be more fruitful. A NRV would solve problems. A
shock arrestor won't help IMHO.


I have just run water through the 'dead' branch I added in preparation
for the en-suite I need to put in (sorry, didn't mention that in my
original post). There was indeed air in the pipe, and getting rid of
this seems to have cured the problem. Hope it stays away now. And many
thanks for all the suggestions!

Johan
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