"John" wrote in message
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"BigWallop" wrote in message
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"John" wrote in message
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"BigWallop" wrote in message
k...

"waddy" wrote in message
oups.com...
Do you need a double check valve when connecting the water mains to a
combi boiler without using any break tank?


Yes. It stops water being sucked back from the heat exchanger in the
boiler,
and, mostly, to stop water getting back to the mains from the filling
hose
to
the central heating loop, which will contain rust inhibitor and other
chemicals.



You can I suppose quote which bylaw asks for this? (The cold mains in to
the
DHW part, the fill loop should include a N/R valve anyway)


Here's just one:
http://www.surreycc.gov.uk/sccwebsit...e?opendocument

But there are plenty more, if you want me to list them for you?


Well I looked at this link but couldn't find anything asking for a N/R
valve on the inlet to a combi (plenty about hoses and horsetroughs which
I'm familiar with). I'm off to look for my copy of the current bylaws but
ISTR (fairly sure) there is no requirement to have a N/R valve on the cold
mains inlet to a combi. Some older combis had an expansion vessel in the
tapwater circuit but later models rely on any thermal expansion of the
potable water relieving back into the pipework. If there was a N/R valve
fitted this would be impossible.

John


Back again. Here's what I was trying to recall:-

Quote-

Backflow prevention

15. - (1) Subject to the following provisions of this paragraph, every
water system shall contain an adequate device or devices for preventing
backflow of fluid from any appliance, fitting or process from occurring.

(2) Paragraph (1) does not apply to-


(a) a water heater where the expanded water is permitted to flow back into
a supply pipe,

end quote