Loosing hot water through Shower pump ??

[Vessy]

Hi,

We have had an issue for a while with the hot water tank not retaining heat very well, decided to have a look last night and found that the cold water feed to the shower pump was hot all the way up to the header tank in the loft!

The shower pump is a twin impeller type, hot at one end of the shaft and cold at the other. Hot water feed comes from a surrey flange to pump then out to the shower mixer, cold feed direct from header tank to pump then out to shower mixer. The shower had not been used for over 12 hours yet the whole assy was hot including the cold water feed pipe.

I shut off the hot feed by means of a gate valve just after the surrey flange and left overnight, this morning the pump assy is cold and so is the cold water feed pipe, this leads me to think I have a convection flow issue.

I can only conclude that it is the pump assy, when I have this convection problem the feed pipes to the shower mixer were both cold so not happening there.

Has anybody seen this problem before, I just cant work out how it is flowing through the pump??