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.
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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