Luke warm water from cold side of mixer tap

[kirks06]

I have an issue where we turn on the cold tap side of a mixer tap and luke warm water appears. In order to get cold water for drinking we need to run the cold tap for at least a minute, wasting loads of water.

This happens across all the mixer taps we have in the house - kitchen; bathroom 1 (bath, not that we drink from the bath tap ! and sink); bathroom 2 (sink); bathroom 3 (sink).

We also have 3 mixer showers in each of the bathrooms.

We have had plumber back to investigate the "luke warm from cold tap issue" as part of much bigger set of issues, where on demanding hot water from any of the showers, not the bath or sink mixer taps, the unvented cylinder system pressure release valve would bounce like a good 'un and vibrate pipework to a level where it would wake the entire house up, not good at 6am when I get up for a shower before work.

The plumber "thought" the issue was a backflow issue due to a faulty mixer cartridge in one of the mixer showers, which he replaced and installed a non-return valve. However, this has not resolved the bouncing valve problem nor the luke warm water issue.

We have lost all faith in the plumber for a number of reasons. But before I engage another plumber I wanted to understand if there is anything I can do to trace which of the mixer taps may be faulty and causing the luke warm water issue.

P.S I work in IT, I am not a plumber, so please please please keep any diagnosis steps to a level where Diane Abbott can understand them ! Thanks Simon

 

[steadyon]

Could be a mains cold pipe run just above a hot pipe for some length. Heat rises from hot pipe and warms water in cold pipe.

Turn off central heating. Avoid drawing off any water, hot or cold, for a couple of hours. Draw cold from a tap. If problem gone, or seems better, could easily be as above.

For the unvented water hammer problem I'd suggest a service of the cylinder by a G3 qualified engineer.

 

[JCplumb]

Could be a mains cold pipe run just above a hot pipe for some length. Heat rises from hot pipe and warms water in cold pipe.

Turn off central heating. Avoid drawing off any water, hot or cold, for a couple of hours. Draw cold from a tap. If problem gone, or seems better, could easily be as above.

For the unvented water hammer problem I'd suggest a service of the cylinder by a G3 qualified engineer.

Beat me to it
I have this issue in my house, hot and cold pipes that feed my bathroom are run through the cylinder cupboard and in boxing. There's the main flow and return for heating in there too. I 'could' re-route the cold feed to the bathroom but I doubt I ever will...