On 07/12/2011 22:58, Tim Streater wrote:
In article ,
John Rumm wrote:

Modern boilers will load sense and modulate - so as the differential
between flow and return falls (which in a correctly working and
balanced system indicates that the house temperature is rising), the
boiler will reduce its output to better match the rate of heat loss
into the house.

You talking about gas or oil, here, John? Or both?

Mostly gas. Some modern oil boilers may be able to modulate, but with
far less range and flexibility compared to a gas one.

Be nice to think an
oil job can vary its output. Otherwise, seems to me, there is a good
risk it just dumps its heat up the flu if the return temp is too high.

Its probably not that bad - as it can't modulate as much, the flow temp
will start to rise and it will then cycle off on its internal stat.
Since the pump will still be running, the hot water in the boiler ought
not be wasted and can still be circulated out to the rads. Cycling like
that is less desirable than a wide modulation range, but it is not the
highly inefficient cycling that one associates with old cast iron
boilers being cycled on the room stat with no pump overrun.


--
Cheers,

John.

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