I’ve been using the Honeywell CM927 (pic below) for many years now just using the standard programme settings.

People on here mention about using Optimum Start features so that the room reaches the required temperature on time. How does this work, as surely it is dependant on the temperature outside the house and how cold the walls are etc. How can it predict how long it will take?

Also our current Veissmann boiler has an external temp gauge on it so it doesnt work as hard as the temp increases, surely this would complicate the Honeywells job further?

So should I select the Optimum Start Feature or leave it alone?

bump…

OK, if it’s like mine (I don’t know the number, it looks the same) then it knows what temperature you want the room to be and the time you want it to be that temperature. It also knows what the current temperature is so the clever bit is that it learns how long it will take to raise the temperature by the required amount and fires up the boiler at the last possible moment to reach the temperature you want on time.

In thoery this means you don’t set the heating to come on earlier than you need just to make sure you aren’t cold. I have no idea how well it works, it sounded good when I bought the heating system and I haven’t given it a thought since 😀

I might just give it a go and see, but still not too convinced its nothing more than a linear graph thats applied.

I can see there will be some calc that basically says that if the room temp is 15 and you want to get to 20 it will take longer than if the room temp is 18 and you want to get to 20…. but surely it cant learn, as I said the enironment outside changes daily so to raise from 15 degress one day will take longer than another, and these systems have no way of knowing if its windy or cold outside?!?

I can appreciate your scepticism but what is the alternative? Always have the heating come on a set time before you actually need it?

As I always say, give it a go you may like it 😉

It ‘learns’ over a series of weeks how long it takes to get the thermostat to set-point.

We’ve got a different controller (with hot water control too), but it’s a Honeywell with a wireless thermostat so presume it works the same way. It does seem to work well, although you have less control over how long your system is actually on for, because it will turn itself on when it thinks it needs to.

It also learns how quickly the house cools down, so will turn the heating off early, so it is still at the set point when the heating is due to go off.
I think you can select whether you use this, or not in the set-up menu.

I was surprised by how often it appears to be ‘optimising’….it flashes up on the display to tell you that it is doing so.

I agree with your comments about not knowing the outside temperature being a hindrance to it’s effectiveness. Perhaps it assumes that the losses to the outside are slow relative to the input period, so are largely irrelevant?
It will use PID control like you get in industrial heater controllers that come with a ‘learn’ setting, rather than just reading off a straight line graph.