On 06/10/2020 20:53, Fredxx wrote:
On 02/10/2020 23:42:17, Fredxx wrote:
On 02/10/2020 23:20:46, wrote:
On Wednesday, 30 September 2020 20:35:29 UTC+1, John SmithÂ* 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.

maybe you could find a similar used one & swap it, but probably you
won't


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...

In most cases a 24kW boiler is not permitted to run on 15mm now,
current regs are more demanding re pressure drop. Worcester Bosch do
a pdf:
Technical Training Bulletin: Natural Gas (G20) Supply Pipe Sizing.
that explains how to calculate what's required.

Do you have a link?

I didn't think so.

I did find this:

http://www.worcester-bosch.co.uk/sup...ownload/TB0053

Although their note that a 24kW boiler's max gas rate is 2.6 m^3/h is
slightly surprising... it would suggest an efficiency of only 80% if its
giving a true 24kW output, and hence drawing gas at a rate of nearly 30kW

(my previous calc was assuming that the input rate is 24kW, which is
likely an underestimate, since most boiler specs now quote output power
rather than input).

Oh, and I missed the brackets round the 6 x 1.9

If I redo my sum with their flow rate, that brings the maximum down to
~4.4m total effective length. (although they also indicate that the
pressure at the boiler inlet only need be 18mBar rather than the 20 one
designs for)



--
Cheers,

John.

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