Water Bye Laws

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:

I think you are confusing the heating circuit, with the DHW mains input. The heating circuit will have a filling loop that incorporates a double check valve. The DHW input does not need one.

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

1. - (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

I'm pretty sure my multipoint water heater (a sort of combi minus the central meating part) explicitly forbids the use of a non-return valve on the mains, as it expects a small amount of expansion back down the mains when you shut off the hot tap and it heats the final cold water entering the heat exchanger.

Thnx John, that will do for me