The bathroom hand basin in my new loft conversion is 300mm higher than
the head of water in the open vented heating system. No problem I
thought just fit a small pump.

Ignoring the problem of 'kick starting' I was convinced that once air
was expelled from the system it would not be a problem.

Unfortunately being a second bathroom the hand basin is not used very
often and develops an air lock which is very difficult to remove.

The pump is a twin impellor (which curiously is cheaper than a single
impellor) with the two inputs and two outputs coupled together. The
feed is 22mm plastic as can be seen in this image:

http://www.flickr.com/photos/8742324...6411/lightbox/

The output is 15mm as can be seen he
http://www.flickr.com/photos/8742324...6279/lightbox/

When the pump is started after a few days rest there is obviously air
around the impellor and a surprisingly large amount of air is expelled
before the thing primes properly. This would be ok but it takes
several gallons of hot water to prime.

I guess the main problem is that the initial output path is downhill
but this is determined by the pump design rather than the
installation. I could fit a vent in the output side but although it
may make 'bleeding' easier it will not stop the problem occurring.

So the obvious questions:

Why does the air reappear?
What can I do to fix it?

Suggestions involving a combi boiler would be sensible but not
appreciated

Brian

On Nov 6, 12:32*pm, Brian Drury
wrote:
The bathroom hand basin in my new loft conversion is 300mm higher than
the head of water in the open vented heating system. No problem I
thought just fit a small pump.

Ignoring the problem of 'kick starting' I was convinced that once air
was expelled from the system it would not be a problem.

Unfortunately being a second bathroom the hand basin is not used very
often and develops an air lock which is very difficult to remove.

The pump is a twin impellor (which curiously is cheaper than a single
impellor) with the two inputs and two outputs coupled together. The
feed is 22mm plastic as can be seen in this image:

http://www.flickr.com/photos/8742324...photos/8742324...

The output is 15mm as can be seen hehttp://www.flickr.com/photos/8742324...photos/8742324...

When the pump is started after a few days rest there is obviously air
around the impellor and a surprisingly large amount of air is expelled
before the thing primes properly. This would be ok but it takes
several gallons of hot water to prime.

I guess the main problem is that the initial output path is downhill
but this is determined by the pump design rather than the
installation. I could fit a vent in the output side but although it
may make 'bleeding' easier it will not stop the problem occurring.

So the obvious questions:

Why does the air reappear?
What can I do to fix it?

Suggestions involving a combi boiler would be sensible but not
appreciated

Brian


If the tap is higher than the supply tank why didn't you buy a
negative head pump in the first place instead of the bodge you have
ended up with?

On Sat, 6 Nov 2010 06:08:32 -0700 (PDT), cynic
wrote:

On Nov 6, 12:32*pm, Brian Drury
wrote:
The bathroom hand basin in my new loft conversion is 300mm higher than
the head of water in the open vented heating system. No problem I
thought just fit a small pump.

Ignoring the problem of 'kick starting' I was convinced that once air
was expelled from the system it would not be a problem.

Unfortunately being a second bathroom the hand basin is not used very
often and develops an air lock which is very difficult to remove.

The pump is a twin impellor (which curiously is cheaper than a single
impellor) with the two inputs and two outputs coupled together. The
feed is 22mm plastic as can be seen in this image:

http://www.flickr.com/photos/8742324...photos/8742324...

The output is 15mm as can be seen hehttp://www.flickr.com/photos/8742324...photos/8742324...

When the pump is started after a few days rest there is obviously air
around the impellor and a surprisingly large amount of air is expelled
before the thing primes properly. This would be ok but it takes
several gallons of hot water to prime.

I guess the main problem is that the initial output path is downhill
but this is determined by the pump design rather than the
installation. I could fit a vent in the output side but although it
may make 'bleeding' easier it will not stop the problem occurring.

So the obvious questions:

Why does the air reappear?
What can I do to fix it?

Suggestions involving a combi boiler would be sensible but not
appreciated

Brian


If the tap is higher than the supply tank why didn't you buy a
negative head pump in the first place instead of the bodge you have
ended up with?

Salamander suggested that this:
http://www.plumbclick.co.uk/gb/product/__534.0015__/
might work but because the negative head is so small it probably would
not.

I thought that my installation looked ok but I guess your standards
must be a lot higher than mine.

It would still be interesting to know where the air comes from.

Brian

On Nov 6, 12:32*pm, Brian Drury
wrote:
The bathroom hand basin in my new loft conversion is 300mm higher than
the head of water in the open vented heating system. No problem I
thought just fit a small pump.

Ignoring the problem of 'kick starting' I was convinced that once air
was expelled from the system it would not be a problem.

Unfortunately being a second bathroom the hand basin is not used very
often and develops an air lock which is very difficult to remove.

The pump is a twin impellor (which curiously is cheaper than a single
impellor) with the two inputs and two outputs coupled together. The
feed is 22mm plastic as can be seen in this image:

http://www.flickr.com/photos/8742324...photos/8742324...

The output is 15mm as can be seen hehttp://www.flickr.com/photos/8742324...photos/8742324...

When the pump is started after a few days rest there is obviously air
around the impellor and a surprisingly large amount of air is expelled
before the thing primes properly. This would be ok but it takes
several gallons of hot water to prime.

I guess the main problem is that the initial output path is downhill
but this is determined by the pump design rather than the
installation. I could fit a vent in the output side but although it
may make 'bleeding' easier it will not stop the problem occurring.

So the obvious questions:

Why does the air reappear?
What can I do to fix it?

Suggestions involving a combi boiler would be sensible but not
appreciated

Brian

Looks like the pump is in the wrong place. Move it close to the hot
water cylinder, then air wont get into the pump to begin with, and you
get virtually instant flow.


NT

On Sat, 6 Nov 2010 06:41:51 -0700 (PDT), Tabby
wrote:

On Nov 6, 12:32*pm, Brian Drury
wrote:
The bathroom hand basin in my new loft conversion is 300mm higher than
the head of water in the open vented heating system. No problem I
thought just fit a small pump.

Ignoring the problem of 'kick starting' I was convinced that once air
was expelled from the system it would not be a problem.

Unfortunately being a second bathroom the hand basin is not used very
often and develops an air lock which is very difficult to remove.

The pump is a twin impellor (which curiously is cheaper than a single
impellor) with the two inputs and two outputs coupled together. The
feed is 22mm plastic as can be seen in this image:

http://www.flickr.com/photos/8742324...photos/8742324...

The output is 15mm as can be seen hehttp://www.flickr.com/photos/8742324...photos/8742324...

When the pump is started after a few days rest there is obviously air
around the impellor and a surprisingly large amount of air is expelled
before the thing primes properly. This would be ok but it takes
several gallons of hot water to prime.

I guess the main problem is that the initial output path is downhill
but this is determined by the pump design rather than the
installation. I could fit a vent in the output side but although it
may make 'bleeding' easier it will not stop the problem occurring.

So the obvious questions:

Why does the air reappear?
What can I do to fix it?

Suggestions involving a combi boiler would be sensible but not
appreciated

Brian

Looks like the pump is in the wrong place. Move it close to the hot
water cylinder, then air wont get into the pump to begin with, and you
get virtually instant flow.


NT
Thanks for that.

I am sure you are correct. The problem then is how to kick start the
pump initially. The small negative head is not enough for flow
switches to detect as there is no movement in the pipe when the tap is
turned on. Also in this instance there is nowhere for the pump to go
on the lower floor.

Incidentally, the bath next to the basin is slightly lower and it
starts ok so as a last resort this could be used to start the basin
but that really is a bodge.

The other obvious suggestion would be to raise the header tank but
there simply is not the room. Lowering the header tank might be
possible but not enough to be sure that a negative head pump will
start.

I can see why every other loft conversion I have looked at has a combi
boiler!

The reason for choosing an open vented system is that the power shower
requirement is far more than a combi could cope with. Also having
recently spent ~ £1000 on the new boiler I am not keen to change it.

Brian

On Nov 6, 12:32 pm, Brian Drury
wrote:
The bathroom hand basin in my new loft conversion is 300mm higher than
the head of water in the open vented heating system. No problem I
thought just fit a small pump.

Ignoring the problem of 'kick starting' I was convinced that once air
was expelled from the system it would not be a problem.

Unfortunately being a second bathroom the hand basin is not used very
often and develops an air lock which is very difficult to remove.

The pump is a twin impellor (which curiously is cheaper than a single
impellor) with the two inputs and two outputs coupled together. The
feed is 22mm plastic as can be seen in this image:

http://www.flickr.com/photos/8742324...photos/8742324...

The output is 15mm as can be seen hehttp://www.flickr.com/photos/8742324...photos/8742324...

can't seemto view those so:-

where is the pump located ?

(ISTR "negative head" pumps are designed for use where the outlet is
in a postion *level with* or above the level of the cold water storage
tank)

Jim K

On Sat, 6 Nov 2010 07:46:47 -0700 (PDT), Jim K
wrote:

On Nov 6, 12:32 pm, Brian Drury
wrote:
The bathroom hand basin in my new loft conversion is 300mm higher than
the head of water in the open vented heating system. No problem I
thought just fit a small pump.

Ignoring the problem of 'kick starting' I was convinced that once air
was expelled from the system it would not be a problem.

Unfortunately being a second bathroom the hand basin is not used very
often and develops an air lock which is very difficult to remove.

The pump is a twin impellor (which curiously is cheaper than a single
impellor) with the two inputs and two outputs coupled together. The
feed is 22mm plastic as can be seen in this image:

http://www.flickr.com/photos/8742324...photos/8742324...

The output is 15mm as can be seen hehttp://www.flickr.com/photos/8742324...photos/8742324...

can't seemto view those so:-

where is the pump located ?

(ISTR "negative head" pumps are designed for use where the outlet is
in a postion *level with* or above the level of the cold water storage
tank)

Jim K

Try these:
http://www.flickr.com/photos/8742324...n/photostream/
http://www.flickr.com/photos/8742324...n/photostream/

The pump is located on the same (first) floor as the taps about 800mm
below the tap.

On Nov 6, 12:32*pm, Brian Drury
wrote:

Suggestions involving a combi boiler would be sensible but not
appreciated

So what about a small "instant" water heater?

MBQ

On Sat, 6 Nov 2010 08:55:35 -0700 (PDT), "Man at B&Q"
wrote:

On Nov 6, 12:32*pm, Brian Drury
wrote:

Suggestions involving a combi boiler would be sensible but not
appreciated

So what about a small "instant" water heater?

MBQ
Now thats a good idea!

A quick browse:
http://www.heatandplumb.com/acatalog...er_Heater.html
suggests that the instant type are rated at about 3.5KW so a separate
feed from the CU will be required.

Best idea so far. Thanks.

Brian

On Nov 6, 12:32*pm, Brian Drury
wrote:
The bathroom hand basin in my new loft conversion is 300mm higher than
the head of water in the open vented heating system. No problem I
thought just fit a small pump.

Ignoring the problem of 'kick starting' I was convinced that once air
was expelled from the system it would not be a problem.

Unfortunately being a second bathroom the hand basin is not used very
often and develops an air lock which is very difficult to remove.

The pump is a twin impellor (which curiously is cheaper than a single
impellor) with the two inputs and two outputs coupled together. The
feed is 22mm plastic as can be seen in this image:

http://www.flickr.com/photos/8742324...photos/8742324...

The output is 15mm as can be seen hehttp://www.flickr.com/photos/8742324...photos/8742324...

When the pump is started after a few days rest there is obviously air
around the impellor and a surprisingly large amount of air is expelled
before the thing primes properly. This would be ok but it takes
several gallons of hot water to prime.

I guess the main problem is that the initial output path is downhill
but this is determined by the pump design rather than the
installation. I could fit a vent in the output side but although it
may make 'bleeding' easier it will not stop the problem occurring.

So the obvious questions:

Why does the air reappear?
What can I do to fix it?

Suggestions involving a combi boiler would be sensible but not
appreciated

Brian

The pump needs to be located in a place well below the water level in
your HW header tank, ie so it is permanently flooded. Ideally below
the bottom of the tank in case it empties completely.
It sounds to me that what is happening is that the water level in the
tank is falling below the pump level when the downstairs bath is
filled. This lets air into the pump.

On Nov 6, 4:24*pm, harry wrote:
On Nov 6, 12:32*pm, Brian Drury





wrote:
The bathroom hand basin in my new loft conversion is 300mm higher than
the head of water in the open vented heating system. No problem I
thought just fit a small pump.

Ignoring the problem of 'kick starting' I was convinced that once air
was expelled from the system it would not be a problem.

Unfortunately being a second bathroom the hand basin is not used very
often and develops an air lock which is very difficult to remove.

The pump is a twin impellor (which curiously is cheaper than a single
impellor) with the two inputs and two outputs coupled together. The
feed is 22mm plastic as can be seen in this image:

http://www.flickr.com/photos/8742324...photos/8742324...

The output is 15mm as can be seen hehttp://www.flickr.com/photos/8742324...photos/8742324...

When the pump is started after a few days rest there is obviously air
around the impellor and a surprisingly large amount of air is expelled
before the thing primes properly. This would be ok but it takes
several gallons of hot water to prime.

I guess the main problem is that the initial output path is downhill
but this is determined by the pump design rather than the
installation. I could fit a vent in the output side but although it
may make 'bleeding' easier it will not stop the problem occurring.

So the obvious questions:

Why does the air reappear?
What can I do to fix it?

Suggestions involving a combi boiler would be sensible but not
appreciated

Brian

The pump needs to be located in a place well below the water level in
your HW header tank, ie so it is permanently flooded. *Ideally below
the bottom of the tank in case it empties completely.
It sounds to me that what is happening is that the water level in the
tank is falling below the pump level when the downstairs bath is
filled. This lets air into the pump.- Hide quoted text -

- Show quoted text -

Oh and some of these pumps don't like to be run dry, they rely on
water to lubricate them.

On Nov 6, 2:14*pm, wrote:
On Sat, 6 Nov 2010 06:41:51 -0700 (PDT), Tabby
wrote:
On Nov 6, 12:32*pm, Brian Drury
wrote:

The bathroom hand basin in my new loft conversion is 300mm higher than
the head of water in the open vented heating system. No problem I
thought just fit a small pump.

Ignoring the problem of 'kick starting' I was convinced that once air
was expelled from the system it would not be a problem.

Unfortunately being a second bathroom the hand basin is not used very
often and develops an air lock which is very difficult to remove.

The pump is a twin impellor (which curiously is cheaper than a single
impellor) with the two inputs and two outputs coupled together. The
feed is 22mm plastic as can be seen in this image:

http://www.flickr.com/photos/8742324...photos/8742324....

The output is 15mm as can be seen hehttp://www.flickr.com/photos/8742324...photos/8742324...

When the pump is started after a few days rest there is obviously air
around the impellor and a surprisingly large amount of air is expelled
before the thing primes properly. This would be ok but it takes
several gallons of hot water to prime.

I guess the main problem is that the initial output path is downhill
but this is determined by the pump design rather than the
installation. I could fit a vent in the output side but although it
may make 'bleeding' easier it will not stop the problem occurring.

So the obvious questions:

Why does the air reappear?
What can I do to fix it?

Suggestions involving a combi boiler would be sensible but not
appreciated

Brian

Looks like the pump is in the wrong place. Move it close to the hot
water cylinder, then air wont get into the pump to begin with, and you
get virtually instant flow.

NT

Thanks for that.

I am sure you are correct. The problem then is how to kick start the
pump initially. The small negative head is not enough for flow
switches to detect as there is no movement in the pipe when the tap is
turned on.

You could just fit a little press switch.


Also in this instance there is nowhere for the pump to go
on the lower floor.

it only needs to go below the water level in the header tank, so floor
level in loft should work.


Incidentally, the bath next to the basin is slightly lower and it
starts ok so as a last resort this could be used to start the basin
but that really is a bodge.

The other obvious suggestion would be to raise the header tank but
there simply is not the room. Lowering the header tank might be
possible

counterproductive

but not enough to be sure that a negative head pump will
start.

I can see why every other loft conversion I have looked at has a combi
boiler!

The reason for choosing an open vented system is that the power shower
requirement is far more than a combi could cope with. Also having
recently spent ~ £1000 on the new boiler I am not keen to change it.

Brian

There's no way the boiler's the problem.

An instant electric heater on the cold feed is another option, but
just moving the pump sounds like all thats needed.


NT

On Nov 6, 1:36*pm, wrote:
It would still be interesting to know where the air comes from.

Maybe dissolved oxygen in the water which comes out of solution when
the pump stops and the pressure drops (although I wouldn't have
thought you'd get enough in the pipes).
There's a lot of dissolved oxygen, most of which appears as bubbles
when the water is heated in the cylinder. For that reason, the
cylinder should have a Surrey/Warix/Essex whatever flange to avoid
drawing the bubbles into the pump.

Do you have a Surrey/Warix/Essex whatever flange?

On 06/11/10 12:32, Brian Drury wrote:
The bathroom hand basin in my new loft conversion is 300mm higher than
the head of water in the open vented heating system. No problem I
thought just fit a small pump.

Ignoring the problem of 'kick starting' I was convinced that once air
was expelled from the system it would not be a problem.

Unfortunately being a second bathroom the hand basin is not used very
often and develops an air lock which is very difficult to remove.

The pump is a twin impellor (which curiously is cheaper than a single
impellor) with the two inputs and two outputs coupled together. The
feed is 22mm plastic as can be seen in this image:

http://www.flickr.com/photos/8742324...6411/lightbox/

That is a Salamander CT50+, a positive head pump. It's not designed for use
in a negative head situation.

You should've installed a negative head pump.

On 06/11/10 13:36, wrote:


Salamander suggested that this:
http://www.plumbclick.co.uk/gb/product/__534.0015__/
might work but because the negative head is so small it probably would
not.


Yes, I'd have thought that would have been a better bet as it is designed to
work in a negative head scenario. The one you did get (CT50+) is a shower
pump and is not designed to work in a negative head scenario at all. You
should have got that one. The SPV pump has a pressure vessel to maintain a
positive pressure to the outlets.

See p5 of http://www.salamanderpumps.co.uk/Dow...structions.pdf

On Sun, 7 Nov 2010 12:33:36 -0800 (PST), Onetap
wrote:

On Nov 6, 1:36*pm, wrote:
It would still be interesting to know where the air comes from.

Maybe dissolved oxygen in the water which comes out of solution when
the pump stops and the pressure drops (although I wouldn't have
thought you'd get enough in the pipes).
There's a lot of dissolved oxygen, most of which appears as bubbles
when the water is heated in the cylinder. For that reason, the
cylinder should have a Surrey/Warix/Essex whatever flange to avoid
drawing the bubbles into the pump.

Do you have a Surrey/Warix/Essex whatever flange?

Thanks to all the respondents.

The suggestion that downstairs is stealing water from upstairs led me
to fit a 22mm one way valve (check valve) as this is easy to do. The
result is no more air in the system.

Incidentally there is indeed a Surrey flange fitted.

So a satisfactory solution to the problem - thank you all.

Brian