Outside tap and double check valve

[rpettipher]

The outside tap at the back of the house has stopped working. Only a trickle of water emerges.
However I can force water back from the tap to the kitchen at the front of the house (and where the water main arrives).
I understand that this should not be possible because there should be a double check valve. Is it possible for such a valve to go faulty and allow water to flow only in the wrong direction?

Unfortunately I cannot find the valve.
The pipe disappears through the back wall of the kitchen cabinet, apparently serving both the outside tap in front of the house as well as that at the rear. A pipe then emerges from the rear wall of the house where the tap is fixed. (Another pipe emerges from the front wall for the front tap.)


The front tap works fine. The front tap also appears to contain a double check valve. The tap at the rear of the house does not - I have removed it from the wall, and still only a trickle of water emerges from the pipe.


Do I have to demolish the back of the kitchen cabinet to get at the pipes or have I missed something?

Thanks for any clues.

 

[ShaunCorbs]

Yes sorry to say somthing definitely wrong if you have had decent flow before if there is a double check fitted may be stuck open a tiny bit allow not much through

 

[rpettipher]

Yes, but it allows a good flow in the wrong direction - seems a strange failure mode ??