On Sun, 9 May 2004 21:37:45 +0100, "Vortex"
wrote:


"Andy Hall" wrote in message
.. .
On Sun, 9 May 2004 20:45:09 +0100, "Vortex"
wrote:

Hi,

Shortly I want to upgrade my gas central heating from "vented" to
"sealed"
(primary reason to eliminate the loft tank to make way for a future loft
conversion.....secondary benefit is that I'll be able to put a rad up
there.)

Both good reasons, and there are several more if you look in Ed
Sirett's FAQ on it.

Yup I've read it. Very useful


You can certainly go larger, and there is no reason not to do so. I
have a boiler with a 10 litre vessel built in, but on calculating the
size, it might have been marginal, so I added another one also of 10
litres.

18 litres it is then. £2.85 more than an 8 litre vessel!!

Exactly, and not really worth doing the sums.



While I'm at it I want to put in "bleed valve" on a spur off the main
boiler
flow (actually this is where the fill and vent pipes will be removed) for
easy introduction of Fernox. Is this normal practice? Seems to make a
lot
of sense to me.

Yes you can do that, although you may prefer to put it at a higher
point. If you are adding a normal system dose of MB-1 it's 4 litres
and depending on layout and drain arrangements, you might not have
enough capacity below this point.

You will also need vents at high points anyway to let air out. These
can be manual or automatic.

Actually I was thinking of the Fernox Gel so the capacity is a non issue
really.

OK. I've tended to use both the inhibitor and the system cleaner in
this range. If you are going to use the gels (and they are a bit
more expensive at around £30 rather than £20) then you don't need a
filling point specifically for the purpose.

Fernox recommends injecting them into a radiator through the vent even
under pressure. That can be messy. What I do is to turn off both
valves on a radiator and drain some water off - I have lockshield
valves with a drain cock on the radiator side on the tail. Then I
inject in the gel - they give you a little tube to do it.

Alternatively, if you are just filling, then inject before adding
water. It is best to fill and check for leaks for a week first
though.

You may find that when you first pressurise that you get some seeping
around spindles of radiator valves. Often, but not always, this can
be corrected by tightening the gland nut. Otherwise, be prepared to
replace.

When I did my system, I decided to replace all the radiator valves
pre-emptively enyway because one or two had shown signs of seeping
with teh open vented system. I used Pegler Terrier valves with
drains as mentioned and Invensys TRV4s for TRVs.




Now I have a new query. I've just been reading the boiler manual (Potterton
Prima F, 10 years old), and for a sealed system the diagram says the Safety
Valve, pressure gauge and axpansion vessel should be connected on the flow
side of the boiler but before the pump (makes sense). It shows the filling
point as being on the "return" side of the boiler. Why? I can see no good
reason.

Generally it doesn't make much difference. I fitted mine where the
header tank used to be.

If you buy a sealed system kit, the pressure gauge, filling connection
point and relief valve all fit to the same manifold.

One important thing is to make sure that you can vent the air
properly.







David


..andy

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