Combi loses pressure....what to do?

Hi,
I live in a 2 bedroom flat which has a 2 year old Vokera Linea combi boiler supplying hot water and central heating to the flat. Recently, it has started to lose its pressure, requiring refilling on a fortnightly basis.
Now I know that this usually means that there is a leak in the system somewhere but all the above-ground pipes are bone-dry and I don't know where to start looking for any leak that may occur under the floorboards.
Does anyone know of any diagnostic tests that I can perform to narrow down the location of any under-floor leak that might exist? It would save me ripping all the flooring up in the flat to no avail.
I also don't much fancy waiting until it's serious enough for my downstairs neighbour to notice - if that ever happens, that is.
Can anyone help?
ta, RM
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Reestit Mutton wrote:

See Below - last line.
--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
  Click to see the full signature.
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Ed Sirett wrote:

Thanks Ed.
As it happens, I found that page late last night via the google news archives...including a couple of posts from you stating that a "once every few weeks" refilling cycle implies a leak so small that it's not worth trying to trace it.
I also read that this problem may be countered to some extent by adding leak sealer to the system. I have my annual boiler service booked in for the beginning of November and I wonder if I can ask the engineer to do this for me at the same time - if so, can you tell me where I might be able to find this stuff (and what exactly I should ask for) so that I can purchase some in advance.
cheers, Laurence.
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Reestit Mutton wrote:

Fernox do some in a yellow cartridge that can be injected into a rad bleed valve. This worked well for me on 2 different systems. Mind you, it ain't cheap rrp 20+. Shop around the sheds/builder merchants to see if there are any special offers, I got mine cheap on a special offer in Travis Perkins. The service engineer may well do it for you but expect to pay another 30 quid for his efforts, when in fact its an easy diy job.
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BillR wrote:

Thanks Bill.
Do these cartridges come with appropriate instructions on how to introduce the chemical into the system?
I assume that I would need to drain the system first?...or can it be administered whilst the system is under normal operating pressure? Does it need any specialist tools to introduce via the bleed valve or is the cartridge all that I need?
If this job is simple enough, I'm sure I can do it myself - I was just thinking that, as my service cost includes up to 1 hour of labour, if it takes significantly less, with a nice smile, a cup o' tea and a biscuit, it may be possible to persuade the engineer to use the spare time to add the inhibitor for me.......wishful thinking, no doubt.
RM
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Reestit Mutton wrote:

Strike that! - I've found the fernox website and it has all the instructions that I need to do the job myself.
ta, RM
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wrote:

Ed's already pointed you in the right direction, I'd just like to add that our system (bokera linea 28) does a similar thing and needs to be topped up perhaps monthly so I've not bothered doing anything about it.
-- cheers,
witchy/binarydinosaurs
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