Baffled By Cylinder Hot Water Draw Whilst Cold Water On

[chloeradhsaw]

I had my indirect hot water cylinder removed a few days ago and the central heating boiler and pump is turned off at the fuse spur right next to the boiler.

I have been without hot water for a few days which is fine - The plumber left the flow / return to the cylinder uncapped as well as the hot water draw off from the cylinder (This is connected to a vent pipe which runs into the cold water storage tank (as it is meant to on a low pressure system).

The cold water to the storage tank is also off as the cold water storage tank is being replaced.

Today I was astonished - I had my cold water kitchen tap open (its a mixer tap) and saw water coming out of the (open) hot water draw off pipe.

See attached

How is it possible for cold water switch on to interfere with hot water ? - If pipe was capped off (and it should have been) it would have gone into the cold water storage right?!

I am quite experienced with heating systems and plumbing but cant figure this out

 

[exedon2]

Back feed from kitchen mixer
Can happen from any mixer tap / shower mixer if no non return valves or if fitted they are sticking.

 

[king of pipes]

As above mains cold water is backing up into the hot supply pipework a professional plumber should know this and cap off any open ends as a precaution. Kop

 

[jerrysmith]

The most likely explanation for what you are seeing is that the cold water supply to your house is pressurized. This means that there is a higher pressure of water in the cold water pipes than in the hot water pipes. When you turn on your cold water tap, the higher pressure of water in the cold water pipes forces some of the hot water out of the hot water draw off pipe.

This is because the hot water draw off pipe is not capped off. If the pipe was capped off, the water would not be able to escape and would instead flow into the cold water storage tank.

To fix this problem, you need to cap off the hot water draw off pipe. This will prevent the hot water from escaping and will allow the cold water to flow freely.

You can also try turning off the cold water supply to your house. This will stop the water from flowing out of the hot water draw off pipe, but it will also mean that you won't have any cold water until you turn the supply back on.