Baxi 105e Hot Water fault

Please help.
Hot water problem with Baxi 105e Instant combi boiler, approx 5yrs old.

When hot tap is opened, boiler fires up and temperature LED's slowly increase to show max. By this time steaming hot water is avialable at the tap, however the boiler will then cut out (ie gas burner shuts down) whilst tap is still calling for hot water. Water at tap then becomes luke warm to cold, no where near enough to run a bath! After about a minute boiler will fire up again but only for a short time, then repeats cycle.
Central Heating side of boiler works fine, apart from slow loss of pressure, which I believed to be down to weak Pressure Relief valve, so this has just been replaced.
I have followed fault diagrams in the manual and have just replaced Hot Water Temperature sensor (part no. 5108265 was 247394). But fault still remains.
Could this be related to the Heat Exchanger?
They are a bit more pricey so would like to try the cheaper options first.

Regards,
Craig

Sounds like a classic case of a blocked plate HE.

To diagnose measure the temperature differential across the primary on the plate. Should be about 10-20°.

Tony

Thanks for the quick response & confirming my guesswork.
I'm just a practical guy prepared to have a go at things, but haven't got any specialist temp testing gear.
Is there any other way to prove it's the HE or is there a possibility it could be anything else?

I replaced loads of parts on my old Saunier Duval combi, so I don't think the job will be out of my league, just trying to prove the correct part to replace.

Thanks
Craig

You can get an idea by hand.

The flow should be too hot to touch and the return almost too hot to touch.

It should be obvious if there is a big temperature difference.

You may be able to clean the plate. Search this site.

Tony