"Tim Downie" wrote in message
...

So you still can't understand the relevance of the difference between a
3kw input and a 10kw input then?

I can't imagine any sealed heat store losing heat faster than a 3 kW heater
can put heat in.
Therefore a 3 kW heater will cause such a system to explode if the safety
measures are disabled.
In fact I have known an /uninsulated/ vented tank boil when an immersion
heater stat went faulty.