Water overflows in attic when i use a garden hose

Harcrid

Hi, I wonder if you can shed some light on my plumbing issue. I do not have an outside tap, so I usually connect to a mixer tap in my back utility room using an adapter whenever i need to use a water hose or power washer. What happens however is that when I close the nozzle of the water hose to turn off the water (but feed on mixer tap is still open), after a few minutes water will pour out of the overflow pipe from the attic tank. This can happen too if I have the water hose only slightly open so I assume there is some backpressure or something allowing the water to flow to the tank. Now that I type this, I realise I have not tried this on another tap in the house so I must do this as a test, but is there any indication as to what may be causing this?

Tow

Water being pushed back up the hot pipe into the cylinder, the cylinder overflows in to the cold tank, the cold tank overflows outside.

magicbastarder

If the mixer tap is mixing hot and cold feed, the pressure in the cold feed is higher than from hot - so when you turn off the hose, the cold pressure forces cold water back up the hot feed and that water is pumped back up through the system, filling your tank to overflow.

Harcrid

Ok thanks for that. So if i was to install an outside tap I most likely would not have this issue since it would only be running directly from the cold feed?

Flinty997

Need a non return value for the feed into the hot water cylinder.

Get an outside tap fitted. It will be cold water only. In

Harcrid

Thanks all. Appreciate it!

blackbox

It shouldn't happen if you keep the hot tap closed.