Combi water temp fluctuates but radiators OK

[AnonymousImport]

Apologies if this has been asked before...
We have an Ocean Alpha240eco Combi boiler. The problem is that we get severe fluctuations in the hot water temperature, however the heating from the radiators is good in all rooms. The water temp (e.g. in the shower) typically will go scalding hot in the first 30 seconds, then drop to lukewarm for a while, only occasionally getting hot again.
This is pretty frustrating. It's not a shower prob - the water temp fluctuates similarly from the other hot water taps too... We are in a bungalow BTW, with the boiler in the loft.

 

[AnonymousImport]

we had that, The solution turned out to be a major part in the boiler, it was not a diy job, i would suggest you call in a corgi registered plumber for a second opinion, then ask for a quote, and then ask another plumber for a third opinion. I was not joking its just that one may say its xyz, the other tuv, but any thing to with a boiler i would recomend a professional