Hi , was the system flushed before the new boiler was installed? If it was then maybe the boiler has a dud part. If it wasn't maybe the domestic heat exchanger is a little blocked. The hot water thermistor can be tested with a multimeter on ohms. It should be within a certain range. I'm wondering if there is a commissioning setting for hot water temp . I will check with baxi this morning. Luckily the boiler is still under warranty for parts and labour. Do you have the exact model number and GC number?
hi thanks for response
complete new system (heating and hot water) installed same time as boiler
system was flushed
boiler is Baxi duo tech HE a 24 combi