The water to the header tank was turned off and the system drained down.
Swapped the mid position vale and it will now not fill back up.
The odd thing is the header tank did not drain off - it was still full
when I went to turn the water on.
There is usually (always?) a manual lever on the valve which allows both
sides to be open and latched to facilitate filling. The latch on the
manual lever should be overriden when the system is in operation by
first switching to CH and then hot water only.
I did. We filled the CH circuit up that way and eventually it started
adding more water to the already full CH header tank via the expansion pipe.
I now realise the logical conclusion at this point would have been to
block the expansion pipe and try to fill the header tank via it's feed
pipe (ie the 15mm gravity feed pipe that the tank uses to feed the CH
pipework from) or in other words (Star Trek and Scotty anyone, just
reverse the gravity laddie) to prove that this pipe was blocked.
Cheers for the help. Much appreciated.
Indeed a well tested solution, but worth mentioning that will clear an
airlock in a vented hot water system, it won't help when there is one in
the vented CH primary. You would need to find a way to connect your cold
water tap to a rad tail or similar to have the same effect there.
Correct and a 15mm gate valve that I did not know (shelves full of
towels etc) between the header tank to the CH pipework (joining into the
CH pipework just below the air separator) that I did know about.
It looks like the valve was not fully open (and has probably been like
that for 20 years) allowing crud and to fill the 15mm feeder pipe.
New gate valve and a bucket of water through the header tank and all is
Thank you to you and everyone else that has helped.
I certainly did not. I have shit loads of the stuff as some new-builds I
was working on had electric only heating. The bathroom and en suite had
water filled towel rads with electric elements and they sent a full
bottle of inhibitor with every house. One bottle did all 20 houses and I
kept the rest:-)
I'm confused! Which bit is gravity? If there's a mid-position valve, the
primary circuit is presumably fully pumped. It may be vented (as opposed
to pressurised) if there's a small fill and expansion tank - but that
doesn't make it "gravity". Is it thins tank which you're referring to as
the header tank, or do you mean the large cold water header for the
(presumably) gravity HW system?
Can you clarify just what you mean by "won't fill back up". Exactly what
is happening or not happening?
As someone else has pointed out, the 3-way valve will be in the HW-only
position when no power is applies to it. The manual lever moves it to
the mid position, when you should get some flow to both circuits. You
may need to do that if the primary circuit won't refill properly.
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