The blue tap test has demonstrated that the obvious cause of a 10° temperature difference between the boiler and hot tap is not a cross coupling.
I am not convinced that your measurements have been meaningful.
Could you do the following test EXACTLY as I have listed it then I can tell you the probable cause.
Set the boiler to DHW only.
Set the shower to hot only and the flow rate to 8 li/min and then measure the temperature at boiler out pipe and then at shower output after its stabilised for a few minutes.
I would remind you I was basing my suggestion on the information that there was a 10°C loss between boiler and bathroom. I am now begining to wonder if this was true.
Tony
I am not convinced that your measurements have been meaningful.
Could you do the following test EXACTLY as I have listed it then I can tell you the probable cause.
Set the boiler to DHW only.
Set the shower to hot only and the flow rate to 8 li/min and then measure the temperature at boiler out pipe and then at shower output after its stabilised for a few minutes.
I would remind you I was basing my suggestion on the information that there was a 10°C loss between boiler and bathroom. I am now begining to wonder if this was true.
Tony