After changing mixer tap in kitchen, turn hot tap on and there was no hot water.Drained hot and cold system then refilled system, this seemed to do the trick for a while then after day or two there was no hot water again.There were no failure lights appearing on front panel.Tried to drain system again but has not worked.
It could be a split diaphragm in the DHW Pressure Differential Valve, check that when you open hot tap the rod in the centre of the Pressure Differential Valve pushes all the way through and makes the switch, if it does not then its probably the diaphragm.
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