Anti back-siphonage valves on Combis

[Chris61]

I wonder if anyone can tell me if it is a requirement (according to Water Byelaws or any other regulation) for combi boilers to be fitted with an anti back-siphonage valve?

If there is such a requirement, are they fitted to the boilers or does the installer have to fit the valve?

Thanks...

 

[James1991]

If it has a built in filling loop then it will have a non return valve fitted internally. All external filling loops come with the valve as part of the kit.
I have seen non return valves fitted to the cold mains below the boiler when there's been a problem with flow switches/sensors being activated when a cold water tap is opened. This can happen when there are issues with dead legs and air pockets on the hot water pipe work.

 

[Chris61]

Thanks. Does this mean under normal circumstances, the mains cold water inlet to a combi will not have a non return valve fitted?

The reason I ask is that the electrical safety standard for boilers, EN 60335-1 requires appliances fed from the water mains to be fitted with a non return valve. If combis are not normally fitted with such a valve, I need to good reason to justify why any boiler I test does not have one fitted.

 

[slapper]

He didn't say they DONT, he said they DO under normal circumstances

 

[Dean744PiN5]

And if you must fit a non-return valve before the cold inlet to a combi you need to fit a mini expansion vessel to allow for the expansion of the hot water otherwise premature failure of components/leaks will become a very real problem.

 

[Chris61]

He didn't say they DONT, he said they DO under normal circumstances

I thought he implied that an internal filling loop will always have a valve fitted but the mains water inlet would only have a valve fitted if there are problems with flow sensors/switches