"John Rumm" wrote in message
...
kmillar wrote:
If my boiler is running, and servicing the central heating, then after
some time the Hot Water is demanded, won't a flush of cold water end up
going through a very hot boiler? (From the HW Flow via common return).

Are boilers designed to cope with this or is there a possibility of
cracking the heat exchanger?

Many combis have a separate heat exchanger for the hot water side
anyway.

I few don't and the main gas heat exchanger has cold fresh water running
through it. It is designed to cop with excessive low temperatures.


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