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Automatic air vents - central heating...



 
 
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  #1  
Old September 27th 08, 01:40 PM posted to uk.d-i-y
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Posts: 673
Default Automatic air vents - central heating...

HI All

I've not used float-type auto air vents before - so I may be doing
something wrong - expert advice welcomed !

Regular readers may recall the saga of my heatpump system - which was
causing the CH header tank to regularly overflow. This was finally
sorted by bleeding trapped air out of the heat store.

Systems looks like a conventional CH boiler - except that the 'boiler'
is a heatpump, and the return from radiator and DHW circuits passes
through a 200 litre, heavily insulated copper 'heat-store' before it
goes back to the heatpump. When the heat pump switches off the system
circulates water from the store through the DHW / CH until it's cooled
sufficiently.

Anyway....

The whole thing's piped up in copper / pex - the circulating pump has a
little brass float-type auto air vent on the highest point of the
circuit - but the feed to the top of the heat store had no such vent.

The only way to bleed the air from the heat store was to slacken off the
compression fitting at the top of the store and wait while the air finds
its way out - necessitates leaning over the store and applying lateral
pressure to the pex pipe to slightly unseat the pipe - a slow and
uncomfortable process!

So - I bought another auto air vent and fitted it as close as possible
to the feed into the heat store - confidently expecting it to vent air
... automatically ....

Trouble is - it doesn't grr
It's still necessary to do the 'lean over the heat store for a hour at a
time to let the air out'....

So - what don;t I understand about using these auto air vents ?
It's fitted pretty much at the high point of the circuit - certainly on
a level with the union into the heat store. Fitted into a 3/4" x 3/4" x
female threaded 'tee' - with the air valve fitted vertical and into the
threaded part of the tee...

Any ideas please ??

TIA
Adrian
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  #2  
Old September 27th 08, 02:08 PM posted to uk.d-i-y
external usenet poster
 
Posts: 2,508
Default Automatic air vents - central heating...


"Adrian" wrote in message
...

Questions:
You have a thermal store/heat bank heated via a heat pump. It serves CH and
DHW via a plate heat exchanger. Is that so?

Is it a pressurised thermal store? Or is it open vented - uses an F&E tank
to top it up?

  #3  
Old September 27th 08, 04:03 PM posted to uk.d-i-y
external usenet poster
 
Posts: 673
Default Automatic air vents - central heating...

HI

Doctor Drivel wrote:

"Adrian" wrote in message
...

Questions:
You have a thermal store/heat bank heated via a heat pump. It serves CH
and DHW via a plate heat exchanger. Is that so?


Not quite.

The heat store is simply a large tank containing water that's circulated
through the radiators / dhw tank. The circulating water is heated by a
heat pump (ground source)


Is it a pressurised thermal store? Or is it open vented - uses an F&E
tank to top it up?


No - not pressurised - it's part of the open f&e-tank-fed heating circuit.

Adrian

  #4  
Old September 27th 08, 05:11 PM posted to uk.d-i-y
external usenet poster
 
Posts: 105
Default Automatic air vents - central heating...


"Adrian" wrote in message
...
HI All

I've not used float-type auto air vents before - so I may be doing
something wrong - expert advice welcomed !

Regular readers may recall the saga of my heatpump system - which was
causing the CH header tank to regularly overflow. This was finally sorted
by bleeding trapped air out of the heat store.

Systems looks like a conventional CH boiler - except that the 'boiler' is
a heatpump, and the return from radiator and DHW circuits passes through a
200 litre, heavily insulated copper 'heat-store' before it goes back to
the heatpump. When the heat pump switches off the system circulates water
from the store through the DHW / CH until it's cooled sufficiently.

Anyway....

The whole thing's piped up in copper / pex - the circulating pump has a
little brass float-type auto air vent on the highest point of the
circuit - but the feed to the top of the heat store had no such vent.

The only way to bleed the air from the heat store was to slacken off the
compression fitting at the top of the store and wait while the air finds
its way out - necessitates leaning over the store and applying lateral
pressure to the pex pipe to slightly unseat the pipe - a slow and
uncomfortable process!

So - I bought another auto air vent and fitted it as close as possible to
the feed into the heat store - confidently expecting it to vent air ..
automatically ....

Trouble is - it doesn't grr
It's still necessary to do the 'lean over the heat store for a hour at a
time to let the air out'....

So - what don;t I understand about using these auto air vents ?
It's fitted pretty much at the high point of the circuit - certainly on a
level with the union into the heat store. Fitted into a 3/4" x 3/4" x
female threaded 'tee' - with the air valve fitted vertical and into the
threaded part of the tee...

Any ideas please ??

TIA
Adrian


Perhaps the air is getting into the tank (ie, as bubbles) faster than it can
go up the vent tube. Only when the water stops circulating will the bubbles
rise to the top. So really you need the vent in the high point of the tank
itself. You can also put it on an extended tube to maximise the volume of
air in the tube instead of in the tank: but obviously you can't go higher
than the header tank, or the float won't float.

We have a float bleed on our ch and it can be tricky to set it up so that
the float doesn't get stuck. Ours has a tyre valve like nipple at the top
which you can depress from the outside to jiggle the float and bleed the air
manually from time to time to make sure it is topped right up. It's very
like an old carburettor float chamber; that one used to have to tickle to
get it to fill right up.

S


  #5  
Old September 27th 08, 05:43 PM posted to uk.d-i-y
external usenet poster
 
Posts: 673
Default Automatic air vents - central heating...

HI S

Spamlet wrote:
"Adrian" wrote in message
...
HI All

I've not used float-type auto air vents before - so I may be doing
something wrong - expert advice welcomed !

Regular readers may recall the saga of my heatpump system - which was
causing the CH header tank to regularly overflow. This was finally sorted
by bleeding trapped air out of the heat store.

Systems looks like a conventional CH boiler - except that the 'boiler' is
a heatpump, and the return from radiator and DHW circuits passes through a
200 litre, heavily insulated copper 'heat-store' before it goes back to
the heatpump. When the heat pump switches off the system circulates water
from the store through the DHW / CH until it's cooled sufficiently.

Anyway....

The whole thing's piped up in copper / pex - the circulating pump has a
little brass float-type auto air vent on the highest point of the
circuit - but the feed to the top of the heat store had no such vent.

The only way to bleed the air from the heat store was to slacken off the
compression fitting at the top of the store and wait while the air finds
its way out - necessitates leaning over the store and applying lateral
pressure to the pex pipe to slightly unseat the pipe - a slow and
uncomfortable process!

So - I bought another auto air vent and fitted it as close as possible to
the feed into the heat store - confidently expecting it to vent air ..
automatically ....

Trouble is - it doesn't grr
It's still necessary to do the 'lean over the heat store for a hour at a
time to let the air out'....

So - what don;t I understand about using these auto air vents ?
It's fitted pretty much at the high point of the circuit - certainly on a
level with the union into the heat store. Fitted into a 3/4" x 3/4" x
female threaded 'tee' - with the air valve fitted vertical and into the
threaded part of the tee...

Any ideas please ??

TIA
Adrian


Perhaps the air is getting into the tank (ie, as bubbles) faster than it can
go up the vent tube.



Hmm - possibly

Only when the water stops circulating will the bubbles
rise to the top. So really you need the vent in the high point of the tank
itself.


That would be ideal - but it seems that the manufacturers of the tank
didn't think of that g

You can also put it on an extended tube to maximise the volume of
air in the tube instead of in the tank: but obviously you can't go higher
than the header tank, or the float won't float.


I'd thought of that - maybe fabricate a nice little 'J-shaped' piece of
copper tube that could connect to the tank inlet, then have a 'tee' so
that the valve can sit a few inches above the tank inlet - and the
return from the heating can come in the short leg of the tee...


We have a float bleed on our ch and it can be tricky to set it up so that
the float doesn't get stuck. Ours has a tyre valve like nipple at the top
which you can depress from the outside to jiggle the float and bleed the air
manually from time to time to make sure it is topped right up. It's very
like an old carburettor float chamber; that one used to have to tickle to
get it to fill right up.


Ah - that takes me back - BSA 350 single - a right pig to start!

Both of these valves have a removable cap on the top - but the odd ting
is that when you remove the cap from the one that's on the heat store
and slide a piece of tin wire down to depress the float there's only a
tiny amount of air that escapes - while loosening the union on the tank
itself allows air out, and you can hear the water trickling inside the
tank.

When I got it sorted the last time (before I drained everything down to
add a proper drain cock and this air-valve) I managed to get it to the
point where the circulating water was silent in the tank - but it took a
couple of hours with the union slackened off and 'jiggling' the pex pipe
to get the air to come out - I was hoping to 'automate' the process!

Before anybody asks g - yes - the air is coming _out_ rather than 'in'
- soap solution blows bubbles when wiped around the loosened union.

Thanks
Adrian
  #6  
Old September 27th 08, 05:45 PM posted to uk.d-i-y
external usenet poster
 
Posts: 2,508
Default Automatic air vents - central heating...


"Adrian" wrote in message
...
HI

Doctor Drivel wrote:

"Adrian" wrote in message
...

Questions:
You have a thermal store/heat bank heated via a heat pump. It serves CH
and DHW via a plate heat exchanger. Is that so?


Not quite.

The heat store is simply a large tank containing water that's circulated
through the radiators / dhw tank. The circulating water is heated by a
heat pump (ground source)


Is it a pressurised thermal store? Or is it open vented - uses an F&E
tank to top it up?


No - not pressurised - it's part of the open f&e-tank-fed heating circuit.


Adrian, where is the thermal store vented from, on the store and where is
the cold feed connected to it?


  #7  
Old September 27th 08, 05:55 PM posted to uk.d-i-y
external usenet poster
 
Posts: 673
Default Automatic air vents - central heating...

HI

Doctor Drivel wrote:

"Adrian" wrote in message
...
HI

Doctor Drivel wrote:

"Adrian" wrote in message
...

Questions:
You have a thermal store/heat bank heated via a heat pump. It serves
CH and DHW via a plate heat exchanger. Is that so?


Not quite.

The heat store is simply a large tank containing water that's
circulated through the radiators / dhw tank. The circulating water is
heated by a heat pump (ground source)


Is it a pressurised thermal store? Or is it open vented - uses an
F&E tank to top it up?


No - not pressurised - it's part of the open f&e-tank-fed heating
circuit.


Adrian, where is the thermal store vented from, on the store and where
is the cold feed connected to it?



The easiest way for me to describe it is....

Imagine a conventional, non-pressurised, boiler system.
Replace the boiler with the Heatpump.
On the return circuit from the radiators / hot-water tank to the
'boiler' (and immediate 'before' the boiler), insert a big water tank -
with the return from the heating circuit piped to the top of the tank
and the return to the boiler piped from the bottom of the tank.

No separate vents or feeds connected to the store.

Heatpump and store are at ground-level, f&e tank is in the loft...

Hope that makes it clearer?

Adrian
  #8  
Old September 27th 08, 07:02 PM posted to uk.d-i-y
external usenet poster
 
Posts: 9,377
Default Automatic air vents - central heating...



"Adrian" wrote in message
...
HI All

I've not used float-type auto air vents before - so I may be doing
something wrong - expert advice welcomed !


The float vent I have in my hand has a screw on the top that appears to
close the vent even if the float is not floating.
I believe it is really for fast filling a pressurised system and not
actually an auto vent to release trapped air.
It looks like you open it to let the air out while filling and then close it
to ensure air can't get drawn in by the circulating water.
Maybe yours is the same and you have it closed?

  #9  
Old September 27th 08, 09:47 PM posted to uk.d-i-y
external usenet poster
 
Posts: 2,508
Default Automatic air vents - central heating...


"Adrian" wrote in message
...
HI

Doctor Drivel wrote:

"Adrian" wrote in message
...
HI

Doctor Drivel wrote:

"Adrian" wrote in message
...

Questions:
You have a thermal store/heat bank heated via a heat pump. It serves
CH and DHW via a plate heat exchanger. Is that so?

Not quite.

The heat store is simply a large tank containing water that's circulated
through the radiators / dhw tank. The circulating water is heated by a
heat pump (ground source)


Is it a pressurised thermal store? Or is it open vented - uses an F&E
tank to top it up?

No - not pressurised - it's part of the open f&e-tank-fed heating
circuit.


Adrian, where is the thermal store vented from, on the store and where is
the cold feed connected to it?



The easiest way for me to describe it is....

Imagine a conventional, non-pressurised, boiler system.
Replace the boiler with the Heatpump.
On the return circuit from the radiators / hot-water tank to the 'boiler'
(and immediate 'before' the boiler), insert a big water tank -
with the return from the heating circuit piped to the top of the tank and
the return to the boiler piped from the bottom of the tank.

No separate vents or feeds connected to the store.

Heatpump and store are at ground-level, f&e tank is in the loft...

Hope that makes it clearer?


As clear as mud. Firstly, is this right? "the return from the heating
circuit piped to the top of the tank and the return to the boiler piped from
the bottom of the tank".

The return from the DHW cylinder and CH to the "top" of the thermal store?
Is that right?

Where is the CH flow connected to the system?
Where is the heat pump's flow connected to the system?

The vent pipe from the F&E tank. Where is it connected to the system?
The cold feed pipe from the F&E tank. Where is it connected to the system?

  #10  
Old September 27th 08, 10:26 PM posted to uk.d-i-y
external usenet poster
 
Posts: 673
Default Automatic air vents - central heating...

HI

Doctor Drivel wrote:

"Adrian" wrote in message
...
HI

Doctor Drivel wrote:

"Adrian" wrote in message
...
HI

Doctor Drivel wrote:

"Adrian" wrote in message
...

Questions:
You have a thermal store/heat bank heated via a heat pump. It
serves CH and DHW via a plate heat exchanger. Is that so?

Not quite.

The heat store is simply a large tank containing water that's
circulated through the radiators / dhw tank. The circulating water
is heated by a heat pump (ground source)


Is it a pressurised thermal store? Or is it open vented - uses an
F&E tank to top it up?

No - not pressurised - it's part of the open f&e-tank-fed heating
circuit.

Adrian, where is the thermal store vented from, on the store and
where is the cold feed connected to it?



The easiest way for me to describe it is....

Imagine a conventional, non-pressurised, boiler system.
Replace the boiler with the Heatpump.
On the return circuit from the radiators / hot-water tank to the
'boiler' (and immediate 'before' the boiler), insert a big water tank -
with the return from the heating circuit piped to the top of the tank
and the return to the boiler piped from the bottom of the tank.

No separate vents or feeds connected to the store.

Heatpump and store are at ground-level, f&e tank is in the loft...

Hope that makes it clearer?


As clear as mud. Firstly, is this right? "the return from the heating
circuit piped to the top of the tank and the return to the boiler piped
from the bottom of the tank".


Absolutely right.


The return from the DHW cylinder and CH to the "top" of the thermal
store? Is that right?


Same as above...


Where is the CH flow connected to the system?


Flow goes from the heatpump, through the rads or dhw cylinder coil, then
back as the return.....


Where is the heat pump's flow connected to the system?


See above


The vent pipe from the F&E tank. Where is it connected to the system?


Top end of the dhw cylinder coil...

The cold feed pipe from the F&E tank. Where is it connected to the system?


Same place as the vent pipe.


Look - I'm clearly not explaining this well - I'll see if I can find
time to sketch the system tomorrow or early next week.

The original question was 'is there something that I don't know about
using automatic air vents on circulating water systems?' - - and it
seems that I maybe need to create a point on the return circuit that is
deliberately higher than the store - but very close to the store, and
fit the air vent there....

Thanks
Adrian
 




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