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.

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