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Old June 13th 21, 11:07 AM posted to uk.d-i-y
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Default New Cylinder needed for system boiler fitting?

On 12/06/2021 22:41, Fredxx wrote:
On 12/06/2021 22:24, Roger Mills wrote:
On 12/06/2021 19:36, Fredxx wrote:
On 12/06/2021 19:14, Roger Mills wrote:
On 12/06/2021 18:15, jkn wrote:
Hi All
**** I am musing about finally replacing our anciente back boiler
(Baxi Bermuda, part of a Plan C system dating back ... quite a bit)

One possibility I am considering is having a system boiler fitted
rather than a combi. On question - would it be necessary/advisable
to replace the cylinder at the same time, or could this be kept?

Thanks & Regards
J^n


I would say that it wouldn't be strictly necessary, but it would be
highly advisable.

The cylinder will almost certainly be the indirect type with a
separate coil inside through which the primary water from the boiler
flows. Whilst would work with a system boiler, it may not work very
well. If is was installed in Baxi Bermuda days it is pretty old and
will likely be scaled up unless you are in a soft water area. Also,
it's unlikely to have a fast recovery coil inside so the domestic
hot water won't be heated anything like as fast as it would be with
a new cylinder. Finally, all recent cylinders are covered with foam
insulation which is likely to be better than fitting a loose jacket
round it.

I'm assuming that you plan to alter the pipework and controls in
order to make it a fully pumped system? Modern low volume boilers
just won't work with gravity circulation HW systems like the old
cast iron lumps did. Unless the pump maintains the flow until the
boiler has cooled a bit after each firing cycle, it will overheat
and trip out due to the residual heat.

The OP could consider S-plan. And if an issue to minimise alteration
of pipework, the OP could have separate pumps for CH and DWH with
non-return valves.


That would make it pretty difficult for pump over-run conditions,
where the boiler needs to control the pump. Not impossible, but lots
of relay logic!


Some heat only boilers don't have a pump over-run facility. The Baxi
EcoBlue is an example.




Fair enough if it can cope with the flow stopping as soon as the flame
stops. But, in any case, the OP was talking about using a system boiler,
which included a pump inside the casing.
--
Cheers,
Roger

  #12   Report Post  
Old June 13th 21, 02:53 PM posted to uk.d-i-y
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Posts: 25,191
Default New Cylinder needed for system boiler fitting?

On 13/06/2021 10:07, Roger Mills wrote:
On 12/06/2021 22:41, Fredxx wrote:
On 12/06/2021 22:24, Roger Mills wrote:
On 12/06/2021 19:36, Fredxx wrote:
On 12/06/2021 19:14, Roger Mills wrote:
On 12/06/2021 18:15, jkn wrote:
Hi All
**** I am musing about finally replacing our anciente back boiler
(Baxi Bermuda, part of a Plan C system dating back ... quite a bit)

One possibility I am considering is having a system boiler fitted
rather than a combi. On question - would it be necessary/advisable
to replace the cylinder at the same time, or could this be kept?

Thanks & Regards
J^n


I would say that it wouldn't be strictly necessary, but it would be
highly advisable.

The cylinder will almost certainly be the indirect type with a
separate coil inside through which the primary water from the
boiler flows. Whilst would work with a system boiler, it may not
work very well. If is was installed in Baxi Bermuda days it is
pretty old and will likely be scaled up unless you are in a soft
water area. Also, it's unlikely to have a fast recovery coil inside
so the domestic hot water won't be heated anything like as fast as
it would be with a new cylinder. Finally, all recent cylinders are
covered with foam insulation which is likely to be better than
fitting a loose jacket round it.

I'm assuming that you plan to alter the pipework and controls in
order to make it a fully pumped system? Modern low volume boilers
just won't work with gravity circulation HW systems like the old
cast iron lumps did. Unless the pump maintains the flow until the
boiler has cooled a bit after each firing cycle, it will overheat
and trip out due to the residual heat.

The OP could consider S-plan. And if an issue to minimise alteration
of pipework, the OP could have separate pumps for CH and DWH with
non-return valves.


That would make it pretty difficult for pump over-run conditions,
where the boiler needs to control the pump. Not impossible, but lots
of relay logic!


Some heat only boilers don't have a pump over-run facility. The Baxi
EcoBlue is an example.




Fair enough if it can cope with the flow stopping as soon as the flame
stops. But, in any case, the OP was talking about using a system boiler,
which included a pump inside the casing.


S-Plan+ with a single pump is easy enough - many system boilers have an
internal bypass valve, and so can cope with occluded flow. The control
systems are also usually clever enough to overrun the pump and keep the
required valves open for long enough after the flame is extinguished.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/
  #13   Report Post  
Old June 13th 21, 05:18 PM posted to uk.d-i-y
jkn jkn is offline
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Posts: 686
Default New Cylinder needed for system boiler fitting?

On Sunday, June 13, 2021 at 1:53:57 PM UTC+1, John Rumm wrote:
On 13/06/2021 10:07, Roger Mills wrote:
On 12/06/2021 22:41, Fredxx wrote:
On 12/06/2021 22:24, Roger Mills wrote:
On 12/06/2021 19:36, Fredxx wrote:
On 12/06/2021 19:14, Roger Mills wrote:
On 12/06/2021 18:15, jkn wrote:
Hi All
I am musing about finally replacing our anciente back boiler
(Baxi Bermuda, part of a Plan C system dating back ... quite a bit)

One possibility I am considering is having a system boiler fitted
rather than a combi. On question - would it be necessary/advisable
to replace the cylinder at the same time, or could this be kept?

Thanks & Regards
J^n


I would say that it wouldn't be strictly necessary, but it would be
highly advisable.

The cylinder will almost certainly be the indirect type with a
separate coil inside through which the primary water from the
boiler flows. Whilst would work with a system boiler, it may not
work very well. If is was installed in Baxi Bermuda days it is
pretty old and will likely be scaled up unless you are in a soft
water area. Also, it's unlikely to have a fast recovery coil inside
so the domestic hot water won't be heated anything like as fast as
it would be with a new cylinder. Finally, all recent cylinders are
covered with foam insulation which is likely to be better than
fitting a loose jacket round it.

I'm assuming that you plan to alter the pipework and controls in
order to make it a fully pumped system? Modern low volume boilers
just won't work with gravity circulation HW systems like the old
cast iron lumps did. Unless the pump maintains the flow until the
boiler has cooled a bit after each firing cycle, it will overheat
and trip out due to the residual heat.

The OP could consider S-plan. And if an issue to minimise alteration
of pipework, the OP could have separate pumps for CH and DWH with
non-return valves.


That would make it pretty difficult for pump over-run conditions,
where the boiler needs to control the pump. Not impossible, but lots
of relay logic!

Some heat only boilers don't have a pump over-run facility. The Baxi
EcoBlue is an example.




Fair enough if it can cope with the flow stopping as soon as the flame
stops. But, in any case, the OP was talking about using a system boiler,
which included a pump inside the casing.

S-Plan+ with a single pump is easy enough - many system boilers have an
internal bypass valve, and so can cope with occluded flow. The control
systems are also usually clever enough to overrun the pump and keep the
required valves open for long enough after the flame is extinguished.
--
Cheers,

John.

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


Hi All
thanks a lot for all the useful comments. I wasn't really expecting to get the nod
towards keeping the current cylinder, but it's useful to get more of an idea of the
various considerations. I do also appreciate that there will need to be some
replumbing...

Also thanks John Rumm as always for his wisdom, and for flagging the S Plan
possibility.

It is partly a matter of location that it leading me to the System Boiler route - also
that (like Tim+) I don't like putting all my eggs in one basket, as it were. Having eyeballed
the current setup again, one concern I have is what to do with the condensate drain.
Running a flue to the outside would be OK, but it is a long way to a drain or soil pipe etc.
Are there any other options here? We have a 'French drain', for instance, and I wondered
if that could be brought in operation...

FWIW one reason for doing this *now* is that the back boiler has starting making
'kettling' noises when it starts up. We've fairly recently set the controller to not put
the radiators on, but I wouldn't have thought that that would have caused any such
issues? It is looking to me that the heat exchanger is really sooted up - I actually
fitted a new thermocouple, and cleaned the jet out, a month or so ago, and it seemed
fine then. I'd quite like to fix/understand that even if we do finally sort out a
new boiler...

J^n
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Old June 13th 21, 06:05 PM posted to uk.d-i-y
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Posts: 43,075
Default New Cylinder needed for system boiler fitting?

In article ,
jkn wrote:
FWIW one reason for doing this *now* is that the back boiler has
starting making 'kettling' noises when it starts up. We've fairly
recently set the controller to not put the radiators on, but I wouldn't
have thought that that would have caused any such issues? It is looking
to me that the heat exchanger is really sooted up - I actually fitted a
new thermocouple, and cleaned the jet out, a month or so ago, and it
seemed fine then. I'd quite like to fix/understand that even if we do
finally sort out a new boiler...


A back boiler type - that gets its air from the room - would need regular
cleaning IMHO. About once a year.

--
*Ever stop to think and forget to start again?

Dave Plowman London SW
To e-mail, change noise into sound.
  #15   Report Post  
Old June 13th 21, 09:14 PM posted to uk.d-i-y
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First recorded activity by DIYBanter: Oct 2015
Posts: 3,366
Default New Cylinder needed for system boiler fitting?

jkn wrote:


FWIW one reason for doing this *now* is that the back boiler has starting making
'kettling' noises when it starts up. We've fairly recently set the controller to not put
the radiators on, but I wouldn't have thought that that would have caused any such
issues?


Well, it could do. Without the radiators acting as a “heat sink”, the heat
exchanger is probably running hotter, especially if your HW system relies
on a simple thermo-siphon to circulate the water to your HW tank.

It is looking to me that the heat exchanger is really sooted up - I actually
fitted a new thermocouple, and cleaned the jet out, a month or so ago, and it seemed
fine then. I'd quite like to fix/understand that even if we do finally sort out a
new boiler...


Sooting isn’t good. Suggests inadequate air supply but a certain amount in
an old open vented boiler is probably normal. A good clean out and
sweeping the chimney wouldn’t go amiss!

Tim



--
Please don't feed the trolls


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Old June 14th 21, 12:05 AM posted to uk.d-i-y
jkn jkn is offline
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Posts: 686
Default New Cylinder needed for system boiler fitting?

On Sunday, June 13, 2021 at 8:14:57 PM UTC+1, Tim+ wrote:
jkn wrote:


FWIW one reason for doing this *now* is that the back boiler has starting making
'kettling' noises when it starts up. We've fairly recently set the controller to not put
the radiators on, but I wouldn't have thought that that would have caused any such
issues?

Well, it could do. Without the radiators acting as a “heat sink”, the heat
exchanger is probably running hotter, especially if your HW system relies
on a simple thermo-siphon to circulate the water to your HW tank.


Actually, that is a fair point - thanks.

It is looking to me that the heat exchanger is really sooted up - I actually
fitted a new thermocouple, and cleaned the jet out, a month or so ago, and it seemed
fine then. I'd quite like to fix/understand that even if we do finally sort out a
new boiler...

Sooting isn’t good. Suggests inadequate air supply but a certain amount in
an old open vented boiler is probably normal. A good clean out and
sweeping the chimney wouldn’t go amiss!
Tim


Yeah - we had similar kettling issues a couple of years ago and my service guy
had to do a lot of soot cleaning, although no-one ever understood quite why
it was so bad. Covid restrictions have meant that we didn't get
them in last autumn. As I mentioned, I had separate reason to take a look
inside a month or so ago. The thermocouple had burnt away and the pilot
light was quite yellow. I replaced the thermocouple and cleaned the jet of
the pilot light (about as far as I would go on my own). At that point, the flames
were pretty clean and I didn't notice any great excess of soot. So it ... feels ...
like this sooting up has occurred quite quickly.

Maybe I will (as a temporary measure) try leaving some rads on as an
experiment.

Useful Tim+, thanks.
J^n




  #17   Report Post  
Old June 14th 21, 11:04 AM posted to uk.d-i-y
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Default New Cylinder needed for system boiler fitting?

On 13/06/2021 16:18, jkn wrote:

Hi All
thanks a lot for all the useful comments. I wasn't really expecting to get the nod
towards keeping the current cylinder, but it's useful to get more of an idea of the
various considerations. I do also appreciate that there will need to be some
replumbing...

Also thanks John Rumm as always for his wisdom, and for flagging the S Plan
possibility.


or even W plan (i.e. 3 port diversion valve rather than a mid position
one) has become more useful again with fast recovery cylinders that can
take the full output of the boiler.

It is partly a matter of location that it leading me to the System Boiler route - also
that (like Tim+) I don't like putting all my eggs in one basket, as it were. Having eyeballed


Yup cylinder (vented or unvented) with an immersion will give you options.

(although to be fair I have one in mine, and the only time ihas been
used was in the first few days after installation of the cylinder before
I had finished the boiler install and require replumb to convert from
vented to unvented etc)

the current setup again, one concern I have is what to do with the condensate drain.
Running a flue to the outside would be OK, but it is a long way to a drain or soil pipe etc.
Are there any other options here?


Yup there are a few - the main requirements for a condensate drain are
that it won't freeze and it won't mind the very slightly acidic
condensate. So taking and mixing it into an outflow from a sink or
washing machine that then goes through the wall in a larger pipe (say
40mm) is fine, or a dedicated pipe. The thing to avoid is taking the
21mm plastic pipe straight outside where it could freeze, or letting it
drip directly onto masonry where it could stain etc.

We have a 'French drain', for instance, and I wondered
if that could be brought in operation...


Yup a soakaway is fine - you are not talking about huge amounts of water
- a few L/hour at most usually.


FWIW one reason for doing this *now* is that the back boiler has starting making
'kettling' noises when it starts up. We've fairly recently set the controller to not put
the radiators on, but I wouldn't have thought that that would have caused any such
issues? It is looking to me that the heat exchanger is really sooted up - I actually


It might be just a lower load on it means its running hotter. Also scale
in the HEX can result in kettling. You could add some "Boiler Noise
Reducer", which normally calms it down a bit.

fitted a new thermocouple, and cleaned the jet out, a month or so ago, and it seemed
fine then. I'd quite like to fix/understand that even if we do finally sort out a
new boiler...


It probably also wants a good sweep out and clean - especially important
if it's not a balanced flue design.



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/
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Old June 15th 21, 11:20 AM posted to uk.d-i-y
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Default New Cylinder needed for system boiler fitting?

On 13/06/2021 13:53, John Rumm wrote:
On 13/06/2021 10:07, Roger Mills wrote:
On 12/06/2021 22:41, Fredxx wrote:



Some heat only boilers don't have a pump over-run facility. The Baxi
EcoBlue is an example.




Fair enough if it can cope with the flow stopping as soon as the flame
stops. But, in any case, the OP was talking about using a system
boiler, which included a pump inside the casing.


S-Plan+ with a single pump is easy enough - many system boilers have an
internal bypass valve, and so can cope with occluded flow. The control
systems are also usually clever enough to overrun the pump and keep the
required valves open for long enough after the flame is extinguished.



Fair enough. But I was replying to another poster who had suggested
keeping the existing 2 circuit pipework with a pump in each circuit.
Using a system boiler in such a setup would be a challenge!
--
Cheers,
Roger
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Old June 15th 21, 11:27 AM posted to uk.d-i-y
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Posts: 4,120
Default New Cylinder needed for system boiler fitting?

On 13/06/2021 16:18, jkn wrote:


FWIW one reason for doing this *now* is that the back boiler has starting making
'kettling' noises when it starts up. We've fairly recently set the controller to not put
the radiators on, but I wouldn't have thought that that would have caused any such
issues? It is looking to me that the heat exchanger is really sooted up - I actually
fitted a new thermocouple, and cleaned the jet out, a month or so ago, and it seemed
fine then. I'd quite like to fix/understand that even if we do finally sort out a
new boiler...

J^n


What colour is the boiler flame? If the HE is sooting up it suggests
that there's not enough oxygen, so the flame will be yellow instead of
blue. Make sure that the air supply to the burner isn't blocked and - if
possible - check the gas pressure at the burner when it's firing.

If the boiler is kettling, that's likely to be due to scale on the
*inside" of the HE rather than soot on the outside. As JR says, there
are additives which will help with that.
--
Cheers,
Roger
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Old June 15th 21, 11:30 AM posted to uk.d-i-y
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Posts: 5,063
Default New Cylinder needed for system boiler fitting?

In article , Roger Mills
wrote:
On 13/06/2021 16:18, jkn wrote:



FWIW one reason for doing this *now* is that the back boiler has
starting making 'kettling' noises when it starts up. We've fairly
recently set the controller to not put the radiators on, but I wouldn't
have thought that that would have caused any such issues? It is looking
to me that the heat exchanger is really sooted up - I actually fitted a
new thermocouple, and cleaned the jet out, a month or so ago, and it
seemed fine then. I'd quite like to fix/understand that even if we do
finally sort out a new boiler...

J^n


What colour is the boiler flame? If the HE is sooting up it suggests
that there's not enough oxygen, so the flame will be yellow instead of
blue. Make sure that the air supply to the burner isn't blocked and - if
possible - check the gas pressure at the burner when it's firing.


If the boiler is kettling, that's likely to be due to scale on the
*inside" of the HE rather than soot on the outside. As JR says, there
are additives which will help with that.


screwfix is a good source - "noise reducer"

--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle


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