Hot Water Only Hot When Two Taps Are Running!

3 Oct 2008
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United Kingdom
Hi, I have a hot water system with solar heating for the water.
The heating works, the hot water is also heating in the cylinder but when I turn on the tap, after initially running hot, it goes to lukewarm.
If I run two hot taps it seems to then be hot but as soon as I turn one off, it goes back to lukewarm again.
There are two 3way grundfos pumps in the loft. One seems to be ticking, the other is silent.
Anyone out there have any good ideas before I take a hammer to it all :)

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would suspect shower/mixer letting by
hi twgas,
I have an aqualisa thermo shower. Do you think I may need to replace the cartridge in it? The people who owned the house b4 me had replaced it at some time in the past as they left the old one here.
its a possibilty, can you isolate the supply(ies) to the shower - then try a hot tap.

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