Worcester Bosch 30CDi Combi Boiler over heating

Anonymous's Avatar (by Gravatar) by Anonymous in  Plumbing » Water » Hot Water 

Looking for a bit of diagnostic help on the following problem. The boiler is a Worcester Greenstar 30i ErP Combi has been working fine for about 3 years up to around 3 weeks ago when the boiler started to over heat (hitting 95deg C limit). This problem occurs whilst filling the bath, which has a larger flow though using the shower and sinks did not show any problems and the central heating is working perfectly.

As the boiler has a LCD display I am able to monitor the temperatures and found the following:
To start with DHW input is at 30 deg C and the flow temp is 40 deg C
I turn on the bath hot tap, which delivers around 7 litres/min and over the next 2 minutes the boiler Flow Temp has hit the 95 deg C limit and the boiler turns off but the DHW has only achieved around 45 deg C.
The boiler shows EA9 276 Flow Sensor Fault.
So far I have replaced the Flow Turbo Sensor and using the Engineer menu activated the Air Purged Mode but the issue remains.
It would appear that the secondary (plate) heat exchanger is not working efficiently possibly due to a flow problem but as I have no figures to compare this with I am unsure.

Has anyone got any temperature comparisons from a similar boiler or any ideas what could cause this problem?

Any help is appreciated

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