Heating works but not hot water

[pathill83]

I have an Ideal combi isar HE 24. Heating works perfectly but hot water does not at all.
Turn any hot tap on and water gets luke warm after about 10 seconds then boiler disengages and water gets cold again.
Been told it could be thermistor, or a couple of other things. Can anyone please help?

 

[Deleted member 120897]

Could be the diverter (more likely than thermistor).