Vaillant Aquaplus storage combi boiler

We're planning to replace a tired old Ariston wall-hung combi, and fancy a Vaillant Aquaplus storage combi boiler.
I've seen precious little mention of them in this newsgroup (just one thread from last August, subject: high flow combi - AquaPLUS), and have a few concerns
The house is a 2 bed Victorian terrace with old cast iron radiators - it won't need anything like the 32kW max CH output, but the aquaplus works down to 10.5kW so I don't think there's a problem with that
I've not bothered with a condensing boiler because the cast iron radiators probably mean a high return temperature (I'll measure it when I get a mo), and we're only staying in the house another 2-3 years, after which we will be renting it out, so won't make enough gas savings to really justify the extra 300 quid
The main reason for choosing an aquaplus is the storage DHW - I like the idea of no heating delay or slugs of cold when turning taps on and off, and we've just fitted an Aqualisa Aquatique shower with a 5" head, which could do with all the hot water flow it can get!
However, both gas and water feeds are not ideal.
The gas is 22mm piping - am I right in thinking that if it's not quite up to the job, the boiler will still run OK, just not reach its full 37kW DHW output?
Similarly the mains water pressure isn't brilliant - if I set the shower to fully cold (so not flow restriction from old boiler), and turn on kitchen tap, the flow drops noticeably (although still a reasonable flow) - again am I right in thinking that the aquaplus will handle this OK and just do the best it can. I notice it has a DHW pump - will this give it an advantage over normal combis at low mains pressure?
In summary, is the aquaplus a sensible choice?
Cheers
--
Ben Mack

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Doh! Just discovered it's a 15mm feed - I assume that'll need replacing
One other question - is it worth putting some kind of anti-scale device in line with the DHW feed?
Cheers
--
Ben Mack

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On Tue, 20 Jan 2004 12:56:22 +0000, Ben Mack

The regulations around gas installations require that their should be no more than 1mB pressure drop between the meter and the appliance when under load. So it's not a case of whether the boiler would underperform - it would fail a test - or rather the installation would.
If the pipe run were *very* short it might be OK, but it's doubtful.
There is a way to calculate if you look at
http://www.cda.org.uk/megab2/build/pub124/default.htm
Section 4.3

As long as it is a phosphor dosing type or an ion exchange softener.

.andy
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