Vaillant Ecofit Pure 830

[Wibbly]

So I have a new installation of an Ecofit Pure 830 with a 10yr guarantee. Reading around, I need to set the CH temp to as low as I can get away with for max efficiency (max condensation), right, with the return pipe temp <55C as a starting point (measured with a thermocouple touching the return pipe where it enters the boiler)? This is despite the Vaillant Advance installer saying they are most efficient when "working hard" at a set point of ~73C ... So I have some questions:

1. I often need a higher temp in this cold weather to get the house to heat up in a reasonable time so setting a low enough return temp will be difficult/marginal. Presumably the return temp will also vary depending on the loss in the house through the rads, as the boiler only maintains the output temp, not the return temp, right? So should I aim to set the boiler temp for a low enough return temp when the house is warm(ish) or cold?
2. Is it would appear to be more efficient to set a lower boiler temp and have it run a lot longer, than a higher temp and have it running for less hrs? What's considered the sweet spot approach if you also consider boiler/pump life etc.? Are lower temps kinder and more efficient all round?
3. The manual says the boiler has an anti-frost feature that kicks in when the water temp drops to, I think, 10C, whereupon it heats the water back up to 35C. I'm often away and have a Nest set to an away/eco temp of 9C in the house. Would you expect things to be more efficient to try and set my away/eco temp above 10C as it seems a waste to have the boiler firing up to get the the water to 35C if that's not contributing to the houses temp anyway - or maybe it is??
4. Is there any solution to figuring out just how much more/less efficient a particular set up is? I can measure overall gas consumption as a result of my fiddling on the meter day by day, but there seem to be too many variables to reliably spot even a few % change due only to my boiler & Nest fiddling. The outside conditions vary day by day (which will affect heat loss from the house and the gas required to reach and maintain any set temp), I have a gas cooker (maybe I need to stop eating during the tests?!), the front door might be opened a few extra times over the period of test (maybe I need to never answer the door), etc. etc.!

Or am I trying to be too analytical? Just set to <55C as a return temp when the house is heating up from cold and just leave it at that and assume 'things are better'?

 

[Last Plumber]

In my opinion the best way to control that is via weather comp (real weather comp not radio smart apps).
Once the installer has set in the right heat curve, you won't need to worry about it unless there is an issue with system design. .

For now I would set the heating flow to 60 C and see how it performs. If there is call for running it hotter, then consider larger rads but ask a heating engineers advice who has been to site.

There are many variables and this is not an exact science outside the lab.

 

[Wibbly]

In my opinion the best way to control that is via weather comp (real weather comp not radio smart apps).
Once the installer has set in the right heat curve, you won't need to worry about it unless there is an issue with system design. .

For now I would set the heating flow to 60 C and see how it performs. If there is call for running it hotter, then consider larger rads but ask a heating engineers advice who has been to site.

There are many variables and this is not an exact science outside the lab.

Indeed. Thanks.

It would be helpful, would it not, if boilers had an option at least to essentially maintain return temps instead of feed temps? You could then have a simple Efficiency vs Temp setting. I wonder why that's not done?

 

[Last Plumber]

Indeed. Thanks.

It would be helpful, would it not, if boilers had an option at least to essentially maintain return temps instead of feed temps? You could then have a simple Efficiency vs Temp setting. I wonder why that's not done?

.
Not really, no.
The return temperature is governed mainly by the heat loss from the system. All systems are different.
Your Vaillant does monitor your return temperature constantly.