It can go cold due to it shower detecting low water pressure (our triton has a flashing light when this happens), theres a small filter on the inlet of the shower unit, ours had a lump of solder almost completelly blocking the inlet to the shower.
HTH
Dox
October 2008
also check your outlet thermal cut out.
splodge
October 2008
It could be due to your sprayhead needs a clean or your water pressure is inadequate.
splodge
October 2008
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