On Sat, 12 Mar 2005 18:41:34 +0000, Tim Smith wrote:



1. I did try to shut off the two valves you mention that arent numbers but
at least 1 of them didnt want to turn at all - so I left them.

It would probably have moved with enough oomph and the right tool, it
hasn't moved probably since the boiler was installed and that was probably
in excess of 10 years ago.


2. I didnt turn off the gas valve (again because I hadnt seen your post).

I was being very cautious. I think you were safer than I made out because
the boiler did not get drained and so little air got in
it. In the worst case where there is too much air the pump ceases to work.
However in this model that would be sufficient to stop the boiler working.


I still need to go round bleeding the radiators and (I guess) filling the
water up a bit again.

Yep, but you might as well add inhibitor first.


Question though, given that in a combi the ho****er and heating are
separate, why didnt the hot water work when I drained the system of water. I
surmise the following - both systems hot water and heating pass over the
same flame. The boiler realises that there is no water in the heating
becuase I drained the boiler as well (since I didnt shut off the two valves)
and refuses to fire up. Is this correct ? Therefore if I had shut off the
two valves, the boiler would still have had water in it and fired up....

In nearly all models the gas heats the primary water and that heats the
domestic HW in a secondary heat exchanger. No primary water means no
heating or HW.

You can add inhibitor any place thats convenient. I usually add it at the
non-bleed end of a convenient rad and let the displaced air out through
the bleed point. You need to have the rad at least partially drained
before adding. See the SealedCH FAQ


HTH