High gas usage

FreeBear

MultiFuelBurner said:

Wow 75oC yep that will probably burn hard and fast when switched on after being off for a the periods you talk about in this post.

At that sort of flow temperature, the return temperature is likely to be around 55-60°C. This will put the boiler well outside condensing mode (assuming a fairly modern boiler) which will ruin efficiency. Turn the flow temperature down to 60-65°C, and there will be a marked increase in efficiency. The boiler may need to run a little longer to get the property up to temperature, so it will take a bit of tuning to find the optimum flow temp.

EssexHebridean

Yep - my boiler (also a Veissmann, but nowhere near as new as yours) is currently set in the region of 60 degrees and I used 287kWh in the first 5 days of this month so I'd say with your settings your use is perfectly possible. Comparing back with last year is one option, but that first few days of December this year was far colder than the same period in 2022 I think, so it may not help much. 

northernstar007

am i the only 1 thats gt my boiler set to max,its worcester 34cdi, and gets upto temp in about an hour from 14ish to 21ish, using 55-80kw per day

rigby44

EssexHebridean said:

Yep - my boiler (also a Veissmann, but nowhere near as new as yours) is currently set in the region of 60 degrees and I used 287kWh in the first 5 days of this month so I'd say with your settings your use is perfectly possible. Comparing back with last year is one option, but that first few days of December this year was far colder than the same period in 2022 I think, so it may not help much. 

Thanks for that, I will lower to 65° and see what the impact is.

What is your water temp set to, out of interest?

rigby44

FreeBear said:

MultiFuelBurner said:

Wow 75oC yep that will probably burn hard and fast when switched on after being off for a the periods you talk about in this post.

At that sort of flow temperature, the return temperature is likely to be around 55-60°C. This will put the boiler well outside condensing mode (assuming a fairly modern boiler) which will ruin efficiency. Turn the flow temperature down to 60-65°C, and there will be a marked increase in efficiency. The boiler may need to run a little longer to get the property up to temperature, so it will take a bit of tuning to find the optimum flow temp.

Thank you. I’ll reduce to 65.

MeteredOut

northernstar007 said:

am i the only 1 thats gt my boiler set to max,its worcester 34cdi, and gets upto temp in about an hour from 14ish to 21ish, using 55-80kw per day

That doesn't really tell us anything other than that lowering your flow temp (and perhaps having to tweak your thermostat and boiler schedule) could save you money. Your kWh per day is meaningless without knowing your house size (both number of rooms and number of inhabitants), insulations levels, working habits (home/office), thermostat details and settings, shower habits, shower type, cooking type etc.

It'd be a rate set of circumstances where running a modern boiler at max is the most efficient thing to do (from a cost perspective), even if it does modulate. You're probably not getting much condensing benefit.

FreeBear

rigby44 said:

FreeBear said:

MultiFuelBurner said:

Wow 75oC yep that will probably burn hard and fast when switched on after being off for a the periods you talk about in this post.

At that sort of flow temperature, the return temperature is likely to be around 55-60°C. This will put the boiler well outside condensing mode (assuming a fairly modern boiler) which will ruin efficiency. Turn the flow temperature down to 60-65°C, and there will be a marked increase in efficiency. The boiler may need to run a little longer to get the property up to temperature, so it will take a bit of tuning to find the optimum flow temp.

Thank you. I’ll reduce to 65.

If you have a smart meter (SMETS2), it is worth signing up to one of the energy apps such as Bright or Hugo. These should be able to display gas usage in 30 min intervals which will give you a better idea of what you are burning. Compare the usage at 75°C for a few days (noting outside temperature & boiler run time) against a few days at a lower flow temperature.

rigby44

Guys/girls,

Any reason why Viessmann recommend 75° on combi boilers, if there’s no chance of it entering condensing mode at that temp?

There must be a reason they advise it?

FreeBear

rigby44 said: Any reason why Viessmann recommend 75° on combi boilers, if there’s no chance of it entering condensing mode at that temp?

Current "wisdom" from many heating engineers is that the CH system runs with a ΔT of 50°C - This is the temperature differential between the nominal room temp of 20°C and a flow temp of 70°C. But there is a growing awareness that lower flow temperatures return a higher efficiency and also provide a migration path to alternative heat sources such as heat pumps. Some of this awareness is down to changes in Building Regulations mandating lower temperature heating systems.

As to why Viessmann recommend 75°C, I can only assume that the author is stuck in old ways of thinking. The factory default (on the 050 at least) is 60°C. And if you have weather compensation enabled, the flow temperature will often be much lower. Viessmann do indeed recommend using weather compensation, so the boiler isn't likely to run at 75°C unless it is exceptionally cold outside.

 

born_again

rigby44 said:

Krakkkers said:

Was the heating on?

Of course not. It would all have to have been clocked up between 5:30-10pm

How cold is house when you get in?
Might be worthwhile leaving heating on @ a lower temp via thermostat, so there is some background heat & then boiler does not have to work as hard, for so long to get house warm.

You have not mentioned house size or how well insulated?