Somewhat inspired by the Which Boiler thread but more what can we get
thread.

My friend has a Powermax thermal store "one box" solution which is Gas
burner, vented thermal store tank and domestic (mains pressure) hot
water heat exchanger all in one box, situated in a large airing cupboard.

This never was very good and has a terrible reputation. (small bore heat
exchanger for the DHW results in rapid furring up in the local hard
water and very poor shower performance - We have descaled it 3 times in
10 years but baths have been a no-no for at least 3 years)

They were regarded as rubbish even in 2009
http://www.powermax-repairs.co.uk/

The upcoming summer seems an ideal time to replace. This will be a
professional job but I would like to be informed on system choices prior
to getting anyone in to quote.

Firstly the owner is anti combi - bad previous experience and suspicion
that the hard water area will clog it up just as it has with the Powermax.

The ideal choice would be to install a conventional boiler which heats a
mains pressure cylinder to provide DHW and plumbs into the existing
vented heating system. Is this a possible configuration, or does the
heating have to be pressurised in this sort of setup? It is feared that
pressurising the heating system will result in leaks in many of the old
(but still serviceable at least at low pressure) radiator valves.

Any suggestions will be welcome.
--
Chris B (News)

On 11/04/2017 09:50, Chris B wrote:

The ideal choice would be to install a conventional boiler which heats a
mains pressure cylinder to provide DHW and plumbs into the existing
vented heating system. Is this a possible configuration, or does the
heating have to be pressurised in this sort of setup? It is feared that
pressurising the heating system will result in leaks in many of the old
(but still serviceable at least at low pressure) radiator valves.

Did that 3 years ago, no leaks even though the rads and valves are 30
years old.

Put solar panels in to hot the water too as a twin coil cylinder isn't
much more expensive than a single coil one and you get RHI payments that
will just about pay for the panel.

In article ,
Chris B wrote:
Is this a possible configuration, or does the
heating have to be pressurised in this sort of setup? It is feared that
pressurising the heating system will result in leaks in many of the old
(but still serviceable at least at low pressure) radiator valves.

No reason why a pressurised system will put more of a load on seals etc
than an open vented one.

--
*Honk if you love peace and quiet.

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

On 11/04/2017 14:00, Dave Plowman (News) wrote:
In article ,
Chris B wrote:
Is this a possible configuration, or does the
heating have to be pressurised in this sort of setup? It is feared that
pressurising the heating system will result in leaks in many of the old
(but still serviceable at least at low pressure) radiator valves.

No reason why a pressurised system will put more of a load on seals etc
than an open vented one.


Really? How would that work?
Only going to run at ~2PSI and remove the bit going to the header tank
so no pressure from gravity?

On 11/04/2017 19:06, dennis@home wrote:
On 11/04/2017 14:00, Dave Plowman (News) wrote:
In article ,
Chris B wrote:
Is this a possible configuration, or does the
heating have to be pressurised in this sort of setup? It is feared that
pressurising the heating system will result in leaks in many of the old
(but still serviceable at least at low pressure) radiator valves.

No reason why a pressurised system will put more of a load on seals etc
than an open vented one.


Really? How would that work?
Only going to run at ~2PSI and remove the bit going to the header tank
so no pressure from gravity?

1 bar pressure is equivalent to a water head of 32 feet IIRC.

So, a typical vented system in a two storey house with expansion tank in
the attic is working at a pressure of say 2/3rds of a bar (that's
downstairs, less upstairs).

A pressurised system needs to work at up to 2-3 bar without spewing
water out, but you might be kind to it and only pressurise to 1-1.5 bar
most of the time.

In article ,
GB wrote:
On 11/04/2017 19:06, dennis@home wrote:
On 11/04/2017 14:00, Dave Plowman (News) wrote:
In article ,
Chris B wrote:
Is this a possible configuration, or does the
heating have to be pressurised in this sort of setup? It is feared that
pressurising the heating system will result in leaks in many of the old
(but still serviceable at least at low pressure) radiator valves.

No reason why a pressurised system will put more of a load on seals etc
than an open vented one.


Really? How would that work?
Only going to run at ~2PSI and remove the bit going to the header tank
so no pressure from gravity?

1 bar pressure is equivalent to a water head of 32 feet IIRC.

So, a typical vented system in a two storey house with expansion tank in
the attic is working at a pressure of say 2/3rds of a bar (that's
downstairs, less upstairs).

A pressurised system needs to work at up to 2-3 bar without spewing
water out, but you might be kind to it and only pressurise to 1-1.5 bar
most of the time.

Mine - three story house - is just tickling over zero on the gauge when
cold, and goes up to about 2 bar when hot. That's what it settled down to
so I've left it to it. Doesn't need topping up.

--
*Eschew obfuscation *

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

On 12/04/2017 01:17, Dave Plowman (News) wrote:
In article ,
GB wrote:
On 11/04/2017 19:06, dennis@home wrote:
On 11/04/2017 14:00, Dave Plowman (News) wrote:
In article ,
Chris B wrote:
Is this a possible configuration, or does the
heating have to be pressurised in this sort of setup? It is feared that
pressurising the heating system will result in leaks in many of the old
(but still serviceable at least at low pressure) radiator valves.

No reason why a pressurised system will put more of a load on seals etc
than an open vented one.


Really? How would that work?
Only going to run at ~2PSI and remove the bit going to the header tank
so no pressure from gravity?

1 bar pressure is equivalent to a water head of 32 feet IIRC.

So, a typical vented system in a two storey house with expansion tank in
the attic is working at a pressure of say 2/3rds of a bar (that's
downstairs, less upstairs).

A pressurised system needs to work at up to 2-3 bar without spewing
water out, but you might be kind to it and only pressurise to 1-1.5 bar
most of the time.

Mine - three story house - is just tickling over zero on the gauge when
cold, and goes up to about 2 bar when hot. That's what it settled down to
so I've left it to it. Doesn't need topping up.


What is it when hot as its been claimed a sealed system doesn't have to
increase the pressure over a vented system.
The pressure in a vented system is the same hot or cold.

In article . com,
dennis@home wrote:
On 11/04/2017 14:00, Dave Plowman (News) wrote:
In article ,
Chris B wrote:
Is this a possible configuration, or does the
heating have to be pressurised in this sort of setup? It is feared that
pressurising the heating system will result in leaks in many of the old
(but still serviceable at least at low pressure) radiator valves.

No reason why a pressurised system will put more of a load on seals etc
than an open vented one.


Really? How would that work?
Only going to run at ~2PSI and remove the bit going to the header tank
so no pressure from gravity?

With a header tank the maximum pressure in the system would be in the
lowest pipes, plus a bit from the pump.

--
*When a man opens a car door for his wife, it's either a new car or a new

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

On 11/04/2017 09:50, Chris B wrote:
Somewhat inspired by the Which Boiler thread but more what can we get
thread.

My friend has a Powermax thermal store "one box" solution which is Gas
burner, vented thermal store tank and domestic (mains pressure) hot
water heat exchanger all in one box, situated in a large airing cupboard.

This never was very good and has a terrible reputation. (small bore heat
exchanger for the DHW results in rapid furring up in the local hard
water and very poor shower performance - We have descaled it 3 times in
10 years but baths have been a no-no for at least 3 years)

They were regarded as rubbish even in 2009
http://www.powermax-repairs.co.uk/

The upcoming summer seems an ideal time to replace. This will be a
professional job but I would like to be informed on system choices prior
to getting anyone in to quote.

Firstly the owner is anti combi - bad previous experience and suspicion
that the hard water area will clog it up just as it has with the Powermax.

The ideal choice would be to install a conventional boiler which heats a
mains pressure cylinder to provide DHW and plumbs into the existing
vented heating system. Is this a possible configuration, or does the
heating have to be pressurised in this sort of setup? It is feared that
pressurising the heating system will result in leaks in many of the old
(but still serviceable at least at low pressure) radiator valves.

Any suggestions will be welcome.

Sounds like an unvented cylinder and a system boiler would be the
solution. The cylinder will be mains on the DHW side, but the heating
coil can be on a sealed on vented primary.

There are still a few unvented boilers about. The Vaillant 400 series
spring to mind.

Having said that, converting to sealed on the primary is not normally a
problem IME. If anything does spring a leak, then chances are it was due
to fail in fairly short order anyway. Just make sure the existing system
is well flushed before installing the new boiler.


--
Cheers,

John.

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

In article ,
John Rumm wrote:
Having said that, converting to sealed on the primary is not normally a
problem IME. If anything does spring a leak, then chances are it was due
to fail in fairly short order anyway. Just make sure the existing system
is well flushed before installing the new boiler.

It also make sense. If you do have a leak, it is limited to the contents
of the system. Unlike with a ball valve fed open tank. There's also
generally no need to pressurise the system to the maximum allowed.

--
*Why don't you ever see the headline "Psychic Wins Lottery"?

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

"Dave Plowman (News)" Wrote in message:
In article ,
John Rumm wrote:
Having said that, converting to sealed on the primary is not normally a
problem IME. If anything does spring a leak, then chances are it was due
to fail in fairly short order anyway. Just make sure the existing system
is well flushed before installing the new boiler.

It also make sense. If you do have a leak, it is limited to the contents
of the system.....

....above the point of the leak.

--
Jim K


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