Vitodens 100W and load modulation

[Junglejames]

So, firstly, hello one and all!

Last year I had a Vitodens 100 combi installed. So believe it must have been the B1KC model?

As is often the case, I thought I had done my homework beforehand. Which to be fair I had. But unfortunately nowhere near enough.
Everything on the whole seems fine.
However, I am now doing a bit more homework on the whole subject, and realising just how much I hadn't realised.
Such things as:
Boiler Plus requirements
Opentherm
Modulating heating loads (I never knew boilers did this!!!)
Plus- exactly what weather comp does.

When I got the boiler fitted, I went with an installer who had done a good job at my brothers place. His preference is pretty much always to fit Vaillant boilers, but I had decided on the 100W.
He wasn't keen at first, as the only one he had previously fitted ended up with a burst rubber pipe. But after all of us doing a bit more homework, we realised the offending pipe was now metal on the current model.
He put himself on the Viessmann course, and all went fine.

However as mentioned, I now realise just how much I was never told.
He was of the opinion Weather comp was a waste of time. I was in agreeance as everything the manufacturers told you about it made it sound like a complete fad. So despite I think coming with the sensor, it isn't fitted.
This forum has since taught me stuff about it that no manufacturer tells you, and I have still only touched the surface.

I also now realise nothing was ever mentioned to me about things like load modulation and Opentherm etc etc. I was of the belief the boiler just stop started as it needed to, depending on the internal temperature. So with my new found knowledge on load modulation, I'm trying to work out how my boiler is meant to work, and that is my question.
Some websites make out that modern boilers, if working with a compatible thermostat (I have a wireless Honeywell model), should modulate the load up and down and avoid stop starting. But looking at instructions for my boiler, it suggests that load modulation only works if you have weather comp fitted. Does anyone know the truth?!!! I've never had to use mine too much yet, as I'm not always home. But I get the impression that whilst it doesn't just send out full heat, it isn't modulating the temp flow too much either. As such it does stop start a lot. Room reaches requested temperature, and it shuts itself off. Drops below requested, and off it shoots again!
Saying that, it is good at keeping a pleasant temperature, and I never have scalding hot radiators, but with extra knowledge, I'm wondering if I'm missing something.
Should I have had the weather sensor fitted afterall?
Should my boiler be able to load cycle with just a room thermostat, or does it need weather comp for this?

Right, end of essay, thanks for reading.

 

[Swwils]

Without opentherm or a weather comp sensor the boiler will not automatically adjust flow temperature based on the actual heating demand.

You need to start with a heat loss calculation and see if your radiators are appropriately sized.

If they are then you may well be able to run much reduced flow temperatures and/or flow rate.

This will ensure your boiler is 1. modulating properly (it probably is doing this already and the model you have is very good for this) 2. actually condensing.

https://www.theheatinghub.co.uk/

can point you in the right direction, the boiler cannot be efficient unless installed properly.

 

[Junglejames]

Most radiators have been changed and were checked for size at the time.
I installed the lower end of the suggested scale as before they were stupidly big.
The 2 main ones downstairs are still originals, and plenty large enough for reduced flow temps. This is where the thermostat is most of the time, so no problem there I don't think.

Right now I'm not 100% sure on Opentherm. When I'm home again i will be checking up on my thermostat/ controller.

So you reckon it should be able to modulate without weather comp?
This is what my homework was suggesting, but the instructions for the model suggested otherwise. Nothing is very clear though.

 

[JohnD]

off topic slightly...

I have an older Vitodens 100, which fits inside a 400mm wall cabinet

I hear the new one is a bit wider

if you have a minute, could you accurately measure the casing of yours for me?

Ta.

 

[Junglejames]

If you can hold on for a month until I get back home, then by all means!! As they say, the best things come to those who wait!

I don't have the latest 2021 version though. It's the one prior to that.

 

[Junglejames]

If you can hold on for a month until I get back home, then by all means!! As they say, the best things come to those who wait!

I don't have the latest 2021 version though. It's the one prior to that.

 

[Swwils]

If you don't know the design flow temperature then there is no way to know if the radiators were sized correctly.

If weather comp has not been installed it is unlikely they are designed for a better flow temp.

If you do opt for opentherm at least you have a boiler than can support most of the protocol. So you will need to get a controller that makes use of that. BUT it will not solve fundamental design or installation problems.

The 200w has better weather comp, the 100w will only really be nice on a modern well insulated build.

 

[Junglejames]

Radiators were an afterthought.

It was a simple case of:
What boiler do you want.
Weather comp is a waste of time.
Here you go. Sorted.

When I did, later on, ask if he could fit new radiators upstairs as well if I purchased some, there was never any mention of doing a full check to make sure everything was correctly sized.

Chances are Opentherm is working, although that is something I need to check later on when I can confirm the model thermostat/ controller I have.

So you suggest then that this boiler can modulate even without weather comp?

Which it does seem to partly do, although I assume weather comp makes the modulation that much better.

Anyway, I suspect the point is rather moot now.

A couple of little points make me realise not to use the same installer again (hiding rubbish underneath floorboards in the airing cupboard, and employing somebody else to come and fit the radiators, who never made a very good job of the pipework).
So I'm pretty much screwed as you just don't know who to get in to do any work now. So I doubt I will get weather comp fitted and rads looked at properly, unless I can know who I can fully trust.

 

[vulcancontinental]

Although I work for a different boiler manufacturer and most of our online webinars are for Gas safe installers we offer three for installers and homeowners; Heating Optimisation and and Efficiency, a Controls Overview and Weather Compensation in Depth. You've just missed this months courses but two are repeated next month. They are brand neutral mostly and deal with principles rather than actual product.

If you're on Facebook look for the Heating System Design Group, the guys that run that are Viessmann aficionado's, I'm not a fan but they love them and will help.

If you want background use these links to register for the courses in November

24th at 7pm Heating Optimisation and and Efficiency
https://carrier.zoom.us/webinar/register/2215979244261/WN_afA5PduzTGaAQegnvbHu8Q

23rd at 4pm Controls Overview (more brand specific so no use with a Viessmann but includes a working demo of OpenTherm)
https://carrier.zoom.us/webinar/register/1016010418540/WN_VkfVx7Z5SceKbyqfGV5LPg

Webinar schedule www.vokera.co.uk/webinars to see when the next Weather Compensation in Depth webinar will be scheduled or write into [email protected] as expressing an interest will bring it forward.

Your boiler does modulate as it approaches the setpoint, i.e. lower flame as temperature rises as standard, what WC or load compensation does is lower the setpoint itself rather than work toward a fixed temperature, this will make the boiler more efficient and becomes more important the less efficient the boiler heat exchanger.

 

[Junglejames]

Ta very much for all that. The weather comp webinar could be interesting.

I thought I was understanding things until you suggested that weather comp and load compensation aims to lower the setpoint.

I understand that with weather comp it pretty much aims for a best case scenario based on its preset curves.

Although more and more I'm realising a simple boiler install was perhaps not the way to go, and a lot more homework was required beforehand.
I just hope I haven't wasted too much money with the radiators I had installed upstairs!!!

When I get back home I will confirm what my controller is capable of, then perhaps look to get someone else round to double check everything, fit weather comp, and give the boiler it's first service.

 

[Swwils]

I linked you to the most trustworthy source imaginable, please give them a message.

99% of installers will not know what to do.

It is likely having weather comp will help.

 

[Junglejames]

I linked you to the most trustworthy source imaginable, please give them a message.

99% of installers will not know what to do.

It is likely having weather comp will help.

You did kind sir, and I thank you for that.
It is actually a website I had been on once or twice as part of my homework.
However once I get home, I will give them a bell.