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

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.
--
Cheers,
Roger

On 12/06/2021 19:14, Roger Mills wrote:
On 12/06/2021 18:15, jkn wrote:
Hi All
Â*Â*Â*Â* 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.

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
Â*Â*Â*Â* 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!

--
Cheers,
Roger

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
Â*Â*Â*Â* 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.

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
Â*Â*Â*Â* 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

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


If your cylinder is as old as the rest of the system it will be wasting a
lot of energy in the summer (when heat leaking out isnt useful). I
personally prefer boiler/tank combinations. Combis are too €œeggs all in
one basket€� for me. A tank with an immersion heater is very useful back-up
in case of boiler breakdown.

Tim

--
Please don't feed the trolls

On 12/06/2021 19:17, Tim+ wrote:
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


If your cylinder is as old as the rest of the system it will be wasting a
lot of energy in the summer (when heat leaking out isnt useful). I
personally prefer boiler/tank combinations. Combis are too €œeggs all in
one basket€� for me. A tank with an immersion heater is very useful back-up
in case of boiler breakdown.

+1

Combis are good where space is a premium.

In article ,
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

A system boiler still needs some form of hot water storage, so your
existing cylinder could be used, assuming it is an indirect type. But if
old, may well not perform as well as a decent new one.

--
*Thank you. We're all refreshed and challenged by your unique point of view

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

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?

If the system controls are updated to modern standards (room stat,
cylinder stat, fully pumped operation) then the existing cylinder would
still work, but not as well as a modern one.

Your existing cylinder is probably a slow recovery indirect type,
ideally suited to drawing a little heat when run in parallel with the
rads. A modern condensing boiler would be better matched with a fast
recovery cylinder run in S plan[1] configuration (so full output of the
boiler directed at the cylinder or the rads, but not usually both at once).

If you have a decent cold mains supply, then you could also consider an
unvented cylinder[2] that will give you mains pressure hot water all
around the house, and no need for a cold cistern in the loft.

[1]
http://wiki.diyfaq.org.uk/index.php/...on es:_S-plan

[2] http://wiki.diyfaq.org.uk/index.php/Unvented_DHW


--
Cheers,

John.

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

In article ,
John Rumm wrote:
Your existing cylinder is probably a slow recovery indirect type,
ideally suited to drawing a little heat when run in parallel with the
rads. A modern condensing boiler would be better matched with a fast
recovery cylinder run in S plan[1] configuration (so full output of the
boiler directed at the cylinder or the rads, but not usually both at
once).

I discovered that my fast recovery one will give a reasonable shower
starting with a cold cylinder. Not quite as hot as I'd normally have, but
OK if in a hurry. A sort of instant heater.

--
*Time is the best teacher; unfortunately it kills all its students.

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