Stuart B wrote:
On Sat, 08 Dec 2007 00:32:00 GMT, geoff wrote:

In message , Stuart B
writes
I have an Alpha CD 32C Boiler and a wireless controller in the hall
which is fitted with a rad which has no TRV .Tonight I happened to
notice that this rad was cold at the top so I bled it and there was
quite a lot of air in it for some reason .

Later on I suddenly realised the flat was getting chilly and on
investigating I found that the controller was calling for heat but
that the rads were all cold .I went to the boiler and it wasn't
providing heat and the pressure was showing as zero and the warning
lights were showing ....I didn't note what the sequence was but I
think it was the sequence that means a low pressure .I topped up the
pressure and everything seems fine now .

It seems too much of a concidence that my bleeding this rad would not
have anything to do with the boiler stopping to operate but I cannot
understand why that would be and I like to know reasons for things
happening .

err ...

you have a leak

The air under pressure in the radiator which you let out meant that the
pressure dropped from marginally above to below that at which the water
pressure switch would allow the boiler to operate.

Have you been round and bled all the radiators again ?

and then repressurised ?

You need to find where the water is getting out and the air getting in -
you are diluting the inhibitor every time you add fresh water to the
system
Thx for that reply.

None of the rads have air in them and there are no obvious leaks (
without lifting boards) .

I now understand about the letting out of air reducing the pressure to
below the acceptable pressure .

As for your suggestion about a leak there might actually be a simpler
reason .The rad in the hall with no TRV is not one that I have
actually touched since the boiler was installed in Feb 2007 until
tonight when I went to get something that was lying beside it ( stuff
I need for jobs I am doing round the house) so it might well have been
overlooked for bleeding when the boiler was put in and has remained
cold since .That might actually have been my fault as I bled some of
the rads and the installer did some so it could have been missed as
each of us thought the other had done it . .

I have only had one occasion to top up the water in the boiler since
it was installed and even that decision was marginal so it seems
unlikely that there IS a leak but I'll keep an eye on things .

I find that in practice over a period of time,especially on a new
install there is a tendency for chemical reactions to turn water into
gases..that where the water is probably going.

Yeah if you flush properly and add inhibitor on installation, it happens
much less....