Storage Tank keeps overflowing

[talorigomat]

We had our storage tanks trained as we are fitting a downstairs toilet and sink. On refilling the system there was a blockage that affected the upstairs bathroom's cold water taps and the toilet. A builder we knew tried to clear the blockage but to no avail. He then rerouted the pipework so that the colder water taps for upstairs are fed directly from the main. The result was that we had water running out of the storage tanks overflow pipe. He then fitted a pressure reducing valve first set to 1 bar and then to 0.5. In either case the storage tank still overflowed although in the case of the latter setting much slower. The builder believes that there is a problem with one of the mixer taps in the upstairs bathroom which is causing the cold water to flow back through the hot water pipes and thus into the storage tank. I'm not too sure.

How can I sort this out? many thanks.

 

[bengasman]

Chances are the builder was not a plumber, and botched the job. It is theoretically possible for this situation to occur due to a failing tap, but extremely unlikely, and the existing design would have had to be rather poor in the first place.

 

[fatplumber]

Many modern mixer taps mix in the body of the tap. If you connect mains water and tank fed hot water to the same tap then you can get mains water forced up iinto the cold water service tank.