Optimising my viessmann boiler

[dormermike]

Hello

Not sure if this is the right place to ask, apologies if not.

Had a viessmann boiler installed in the summer and looking at my gas usage it's not using much less than my old non condensing 36kw cast iron 1990s lump. The new boiler is 32kw, so perhaps that's why, and it's not been setup particularly with heat loss etc, so I'm wondering if it's even condensing. It does modulate nicely down, seen it around 8%, but I don't think that means it's condensing, or does it?

How can I tell if it's running optimally ? I didn't particularly change it for efficiency as my old one was running fine, but I needed the room and it was a good a time as any to upgrade. But obviously if I can get it running at it's A rating that would be nice.

Where should I start ? I don't even know what return temps are or how to check, but the flow is currently as shown in image.

It's not setup for weather comp, just an internal sensor.

Thanks

 

[flameport]

I'm wondering if it's even condensing.

With that ridiculously high flow temperature of 73.6C, not it is not.

 

[Johntheo5]

Hello

Not sure if this is the right place to ask, apologies if not.

Had a viessmann boiler installed in the summer and looking at my gas usage it's not using much less than my old non condensing 36kw cast iron 1990s lump. The new boiler is 32kw, so perhaps that's why, and it's not been setup particularly with heat loss etc, so I'm wondering if it's even condensing. It does modulate nicely down, seen it around 8%, but I don't think that means it's condensing, or does it?

How can I tell if it's running optimally ? I didn't particularly change it for efficiency as my old one was running fine, but I needed the room and it was a good a time as any to upgrade. But obviously if I can get it running at it's A rating that would be nice.

Where should I start ? I don't even know what return temps are or how to check, but the flow is currently as shown in image.

It's not setup for weather comp, just an internal sensor.

Thanks

Your fluegas temperature of 68.4C means its not condensing but should still be saving 7 to 10% over your last boiler.
Reduce the flowtemperature to 65C but no lower if you have a HW cylinder with its cylinder stat set to 60C, the rads should really be balanced to give ~ 15C dT, (difference between flow & return). Condensing doesn't really begin until a flue gas temperature of 55C or less.
It was modulating at 41% which means a output/heat demand of 32x41%, 13.1kw.

 

[dormermike]

Your fluegas temperature of 68.4C means its not condensing but should still be saving 7 to 10% over your last boiler.
Reduce the flowtemperature to 65C but no lower if you have a HW cylinder with its cylinder stat set to 60C, the rads should really be balanced to give ~ 15C dT, (difference between flow & return). Condensing doesn't really begin until a flue gas temperature of 55C or less.
It was modulating at 41% which means a output/heat demand of 32x41%, 13.1kw.

Thank you. Any idea how to change the flow temp to 65c? I've read the manual, think I know how to do it tbh, but the viessmann servers are down at the moment so I can't access vicare. I'll wait till they're back up before changing anything.

As an aside they go down a lot "for maintenance". I really must find a better solution. Love the boiler, as much as one can love a boiler, but viessmann really don't know much about how to release software.

 

[dormermike]

I've found how to set my max flow temperature. Its set to 82c which is the factory default. Its a combi (storage) boiler - i'll set it down to 65c as suggested, but i'm wondering why it'd be 82c from the factory if that means it never condenses?

Any how, this looks better, but i may still lower the max flow temp down from 65c to 60c and see how it goes.

 

[dormermike]

This looking better I think? Or flow temps too low?

 

[hllns]

I've found how to set my max flow temperature. Its set to 82c which is the factory default. Its a combi (storage) boiler - i'll set it down to 65c as suggested, but i'm wondering why it'd be 82c from the factory if that means it never condenses?

Because a load of people don't give a crap, there's endless numbers of installs where the boiler's too big with load of stuff set to defaults as it easiest to just sling a new boiler in and be on their way without bothering to look at anything else.

 

[Why Not Indeed]

i'm wondering why it'd be 82c from the factory if that means it never condenses?

Because:
a) You pay the gas bills, not anybody else, so they don't care
b) If the installer sets a sensible flow temperature on the boiler post-install then turns it on and demonstrates it, the most likely response from many will be "but it's so much slower than the old one to warm up!".

Most people don't understand what they're buying and how to use it , and don't have a heat-loss survey done when replacing a boiler, so just replace it with something similar to before. I didn't, and not one of the four companies who quoted to replace mine mentioned it.

 

[dormermike]

Because:
a) You pay the gas bills, not anybody else, so they don't care
b) If the installer sets a sensible flow temperature on the boiler post-install then turns it on and demonstrates it, the most likely response from many will be "but it's so much slower than the old one to warm up!".

Most people don't understand what they're buying and how to use it , and don't have a heat-loss survey done when replacing a boiler, so just replace it with something similar to before. I didn't, and not one of the four companies who quoted to replace mine mentioned it.

Yeah, I didn't get any heat loss calc done either, and that included 2 heat geeks firms. One firm in fairness told my i needed max 18kw for the house, but without asking any questions about insulation etc i'm not sure how they arrived at that figure (well, actually, do know, it was a guestimate).

The guys that actually got the work were the cheapest by far (like, half the price from the highest quote, literally), but were also the most helpful, and a small local firm, so i went with them.

This 32kw (combi) definitely warms the house up slower than my old ideal mexico 36kw floor standing boat anchor, but that's because the new boiler insists on modulating the flow temps as the rads come up to temp. I haven't noticed a difference tbf since setting the flow to 65c from 80c.