In article 2020093020352434361-nospam@nospamcom,
John Smith wrote:
On 2020-09-30 18:58:53 +0000, John Rumm said:

With modern modulating boilers that is less of a problem in the past. A
boiler with a wide modulation range is also desirable. The Vaillant
24kW models often go do to around 6kW.

John, thanks for your suggesting about the PCBs but at 20 years old I
think it's time to replace the whole thing and also it will be quicker.

One possible problem regarding rating and the way new boilers work -
our gas supply pipe to the current boiler is 15mm - is this likely to
be a problem for a condensing system boiler - I know it would be for a
combi boiler. Maybe there is a ceiling on rating or some makers only
specify 22mm.

Digging up the kitchen floor is not a great option...

we have a 75kW boiler with a 22mm supply. The boiler specification sheet
should tell you the size of supply pipe needed.

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