In an earlier contribution to this discussion,
Angela wrote:


That was a very useful post thank you Matthew. I "think" I now
understand what is happening. This is a new house with a new boiler
but I notice that the CM67 isn't sold any more - the
developers/installers must have had a job lot to get rid of. It
seems fine though. I have only just started putting the central
heating on proper and it would appear that this thermostat can
"learn" and I probably haven't given it time to do that. I'll leave
it at the defaults for now and see how things go I think.

Angela

Yes, you won't get a better explanation than that provided by Andy Hall.

As a matter of interest, does your CM67 have Optimum Start and, if so, is it
turned on?

[In case you're not familiar with it, Optimum Start is a feature whereby you
specify the time by which the house should be warm rather than the time at
which the heating should be switched on. The CM67 then decides when to
switch on, so it does it later in mild weather and earlier in cold weather -
helping to conserve fuel. It does this by 'learning' the rate of temperature
rise when the heating is on, so - depending on the starting temperature - it
knows how long it will take to get up to the required temperature. I have it
on mine, and I *think* it's a good thing - but it does sometimes seem to
turn the heating on *very* early in cold weather.]
--
Cheers,
Roger
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