Boiler Mate OV A Class Very Limited Hot Water

Hi

I have a Gledhill Boiler Mate OV A class linked to an Ideal Icos Boiler. House is 6 years old and we can now only get hot water to shower and bath if we have water running at a trickle! If we try to increase flow to either then water goes luke warm then cold and never gets hot again.
Flow rates to both can be good if we want to put up with cold water!
Have no problems with central heating just hot water. We don't have a water softener in the house, so I was thinking of getting the heat exchanger descaled or replaced.
Any thoughts/suggestions would be greatly appreciated
Thanks
Andy

If you read your manual.
You can check for any fault codes ref sensors etc.
Have you checked that the DHW pump is free running?
Have you checked the voltage when running a tap?
Depending on how hard your water is 6 years is not that long.
If your PHE is scaled up the flow rate from the hot tap would / could be restricted.
But it does not sound that it is to me.
It could be the other side of the PHE blocked with sludge etc.
Have you carried out any checks?
Have you gone through the post on here.
Look at the BM 2000 one too as they are very similar / same PHE
Mike
MGC/H2O
Norfolk.