Vailllant VCW242 EH - hot water luke warm NOT hot

[seanyboy]

I have a vaillant VCW242 EH boiler that I does not heat the water high enough. The heating works fine, but the hot water takes a long time to run and is just luke warm when it arrives.

The burner responds when a tap opens.
The water section is open full and not seized.
The pressure remains at 1 bar.
The mains pressure to the boiler is good.

Any ideas ?
Thanks

 

[namsag]

Water to water heat exchanger scaled up and not transfering heat properly, you probably still have the original black plastic one this has been changed to more modern plate type

 

[DP]

How much water runs from hot tap in a minute? Should be 9.5 liters.

 

[seanyboy]

The heat exchanger is the the new modern plate type and water flowing at just under 9L minute.

The problem occured when a kitchen fitter put a new tap on and adjusted the DHW temp dial for some reason, the DHW was fine before that.

 

[seanyboy]

I have found that when you turn the hot tap on full and then back by half after 10 seconds the water heat increases however if I reduce the mains pressure to the boiler the burner does not light with lower pressure. Is this a flow problem or could it be a DHW mirco switch problem ?