I've been reading past posts to try to get a feel for which condensing
boilers are currently on the recommended list. However, descriptions
like 'system boiler' and 'heating boiler' seem to have variable meanings.

If I've got it right, a 'heating boiler' has one flow and one return and
any pump(s) must be installed within the piping whereas a 'system
boiler' has two flow and two return, one pair for central heating and
one pair for domestic hot water, both of which have a pump already
installed within the boiler casing.

Anyone care to clarify/correct me?

--
F

(Beware of spam trap - remove the negative)

In article , F
wrote:
If I've got it right, a 'heating boiler' has one flow and one return
and any pump(s) must be installed within the piping

Generally true (though some boilers have two flow and return
connections)

whereas a 'system
boiler' has two flow and two return, one pair for central heating and
one pair for domestic hot water, both of which have a pump already
installed within the boiler casing.

You're confusing a system boiler and a combi. A system boiler includes a
pump and will have flow and return connections like any other boiler. A
combi adds main cold water in and DHW out to serve the hot water taps,
the hot water being heated when required.

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk
Free SEDBUK boiler database browser http://www.sda.co.uk/qsedbuk.htm
[Latest version QSEDBUK 1.10 released 4 April 2005]

On 07/07/2005 12:23 Tony Bryer wrote:

You're confusing a system boiler and a combi. A system boiler includes a
pump and will have flow and return connections like any other boiler. A
combi adds main cold water in and DHW out to serve the hot water taps,
the hot water being heated when required.

I understand combis (I think!): they heat cold water straight from the
mains and send it straight to a hot tap. The heated water isn't stored.

Are you saying that the only difference between 'system' and 'heating'
is the presence of a pump within the casing?

--
F

(Beware of spam trap - remove the negative)

In article ,
F wrote:
Are you saying that the only difference between 'system' and 'heating'
is the presence of a pump within the casing?

System boilers are everything in one box, so beloved of our resident self
appointed pro heating engineer, Drivel, who can't do even simple pipework
without leaks. And wiring just plain terrifies him.

--
*Never kick a cow pat on a hot day *

Dave Plowman London SW
To e-mail, change noise into sound.

"F" wrote in message
...
On 07/07/2005 12:23 Tony Bryer wrote:

You're confusing a system boiler and a combi. A system boiler includes a
pump and will have flow and return connections like any other boiler. A
combi adds main cold water in and DHW out to serve the hot water taps,
the hot water being heated when required.

I understand combis (I think!): they heat cold water straight from the
mains and send it straight to a hot tap. The heated water isn't stored.

Er, er, I don't want to confuse matters, but in some, hot water is stored,
but all inside the same one-box case.

Are you saying that the only difference between 'system' and 'heating'
is the presence of a pump within the casing?

A system has a pump and a pressure vessel. A heating boiler "genrally" has
none. Although some makers may incorporate a pump in some cases.

A system boiler is an on-demand combi without the water section.

"Dave Plowman (News)" wrote in message
...
In article ,
F wrote:
Are you saying that the only difference between 'system' and 'heating'
is the presence of a pump within the casing?

System boilers are everything in one box

No. The DHW is not catered for, combi's do that.

snip senile electric caber tossing drivel

F wrote:

I've been reading past posts to try to get a feel for which condensing
boilers are currently on the recommended list. However, descriptions
like 'system boiler' and 'heating boiler' seem to have variable meanings.

To some extent that is true - they are not exactly defined terms.

If I've got it right, a 'heating boiler' has one flow and one return and
any pump(s) must be installed within the piping whereas a 'system

That is usually the case - the components required to make a complete
system need to be added; typically a pump, sealed system expansion
chamber, and any valves and controls circuits required.

boiler' has two flow and two return, one pair for central heating and
one pair for domestic hot water, both of which have a pump already
installed within the boiler casing.

A system boiler may only have one flow and return (and a heating only
boiler may have two!). It will almost certainly have a pump, it will
probably have the expansion vessel. What else it contains will vary from
one make/model to the next. As a general rule however you will need to
add fewer external components to form a working system.

Anyone care to clarify/correct me?

Any better?


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

A system boiler is an on-demand combi without the water section.

Not according to Worcester Bosch!

Their definition of a system boiler seems to cover boiler, pump and
expansion vessel but not necessarily with water heating combi facility.

From their website:

The Greenstar 28 HE System is suitable for a medium/large family
house. As this boiler uses a hot water storage cylinder, the cylinder
capacity determines how many bathrooms can be used.

Phil

Are you saying that the only difference between 'system' and 'heating'
is the presence of a pump within the casing?

A system boiler also includes the components for sealed pressurised
operation, such as pressure relief, expansion vessel, filling loop, pressure
gauge etc. Some don't include a pump, although the vast majority do.

Christian.

On Thu, 07 Jul 2005 12:48:20 +0100, F wrote:

On 07/07/2005 12:23 Tony Bryer wrote:

You're confusing a system boiler and a combi. A system boiler includes a
pump and will have flow and return connections like any other boiler. A
combi adds main cold water in and DHW out to serve the hot water taps,
the hot water being heated when required.

I understand combis (I think!): they heat cold water straight from the
mains and send it straight to a hot tap. The heated water isn't stored.

The better models have a store to assist with short term flow rate.


Are you saying that the only difference between 'system' and 'heating'
is the presence of a pump within the casing?

In many cases: yes. However it is common to also find that a system
boiler will also include the components for a Sealed system. See FAQ.

--
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

"Doctor Evil" wrote:

A system boiler is an on-demand combi without the water section.

Utter Bull****, go back and read your leaflets you moron

--

Matt wrote:
"Doctor Evil" wrote:


A system boiler is an on-demand combi without the water section.


Utter Bull****, go back and read your leaflets you moron

I'm sorry but as I have fitted 2 system and 1 combi I agree with Dr
Evil. System boilers I've looked at were nothing but combis without the
DHW section. As they are not so popular they are not so competitively
priced as combis so the next one I need will be a combi with the DHW
ignored or just feeding the kitchen tap.

"Matt" wrote in message
...
"Doctor Evil" wrote:

A system boiler is an on-demand combi without the water section.

Utter Bull****, go back and read your leaflets you moron

Another lunatic who hasn't a clue.

"OldBill" wrote in message
...
Matt wrote:
"Doctor Evil" wrote:


A system boiler is an on-demand combi without the water section.


Utter Bull****, go back and read your leaflets you moron

I'm sorry but as I have fitted 2 system and 1 combi I agree with Dr
Evil. System boilers I've looked at were nothing but combis without the
DHW section. As they are not so popular they are not so competitively
priced as combis so the next one I need will be a combi with the DHW
ignored or just feeding the kitchen tap.

Yep a common ploy. Or have the combi do the shower - high pressure.

"John Rumm" wrote in message
...
F wrote:

I've been reading past posts to try to get a feel for which condensing
boilers are currently on the recommended list. However, descriptions
like 'system boiler' and 'heating boiler' seem to have variable
meanings.

To some extent that is true - they are not exactly defined terms.

They are, a system boiler is very specific.

"TheScullster" wrote in message
...

A system boiler is an on-demand
combi without the water section.

Not according to Worcester Bosch!

Their definition of a system boiler
seems to cover boiler, pump and
expansion vessel but not necessarily
with water heating combi facility.

That is what I said. Read again.

From their website:

The Greenstar 28 HE System is suitable for a medium/large family
house. As this boiler uses a hot water storage cylinder, the cylinder
capacity determines how many bathrooms can be used.

Phil

"Matt" wrote in message
...
"Doctor Evil" wrote:

A system boiler is an on-demand combi without the water section.

Utter Bull****, go back and read your leaflets you moron

Ah Matt, the one who crops with many names to throw abuse. Hi Matt, how is
the cylinder business? Feeling the pinch from combi's eh.

Doctor Evil wrote:

To some extent that is true - they are not exactly defined terms.


They are, a system boiler is very specific.

If that were true then all system boilers would contain the same
components. However they don't.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

"John Rumm" wrote in message
...
Doctor Evil wrote:

To some extent that is true - they are not exactly defined terms.


They are, a system boiler is very specific.

If that were true then all system boilers would contain the same
components. However they don't.

Pump and sealed system componets.