Vaillant 831 vs Worcester-Bosch 30Si vs ?
Kostas Kavoussanakis
Our 25-yo Netaheat suffered a fault last night. It turns out it's the
fan and we decided to have it fixed for one last time.
My very friendly installer only does the Vaillant 831 and the
Worcester-Bosch 30Si, and as I would prefer to use his services, I
thought I would investigate. If I read their specs well (I could not
find much on the Vaillant website) they are pretty marginal for my
property (3 bed detached, 2 baths, Scotland; the W-B site recommended
the 42CDi or the Highflow 440CDi), but let's not dwell on that.
When the time comes, I would like to get something that will last, is
proven but reasonably state of the art and is good value for money. In
terms of cars, I would buy Honda post face-lift, not Rolls, nor Lada
and I buy used.
Back to boilers, in terms of features, I (think) I would like weather
compensation, for example. Also, they both appear to modulate, but who
can tell how low they modulate? I also (think I) would like stainless
steel exchangers; have these got them?
Importantly, how reliable are these? I understand they are pretty
popular brands, so spares are unlikely to be a problem. And that's a
big thing; I had a look at Broag (hail Dr Drivel) for example and they
don't appear to have installers north of Hadrian's Wall.
Thanks in advance,
--
Kostas
John Rumm
>
> Our 25-yo Netaheat suffered a fault last night. It turns out it's the
> fan and we decided to have it fixed for one last time.
>
> My very friendly installer only does the Vaillant 831 and the
> Worcester-Bosch 30Si, and as I would prefer to use his services, I
> thought I would investigate. If I read their specs well (I could not
> find much on the Vaillant website) they are pretty marginal for my
Try here, for full installation instructions:
and here for the controls:
http://www.vaillant.co.uk/installers/heating-solutions-1/controls-and-diagnostics/controls-2/
> property (3 bed detached, 2 baths, Scotland; the W-B site recommended
> the 42CDi or the Highflow 440CDi), but let's not dwell on that.
Marginal for hot water or for heating?
> When the time comes, I would like to get something that will last, is
> proven but reasonably state of the art and is good value for money. In
> terms of cars, I would buy Honda post face-lift, not Rolls, nor Lada and
> I buy used.
>
> Back to boilers, in terms of features, I (think) I would like weather
> compensation, for example. Also, they both appear to modulate, but who
> can tell how low they modulate? I also (think I) would like stainless
> steel exchangers; have these got them?
The vaillant's have SS HEs, the WB's use silicon coated ali. Modulation
range is something like 3:1 IIRC on both (so a 24Kw unit will go down to
8kW). I think you probably need the WB CDi range to support the posher
controls like weather compensation - although that may only apply for
split temperature operation with a cylinder rather than a combi)
> Importantly, how reliable are these? I understand they are pretty
> popular brands, so spares are unlikely to be a problem. And that's a big
Difficult to sort opinion from data here, but they seem to be up the
better end of the market. The Vaillants also support quite detailed
internal diagnostics (accessed via a USB port and PC based software).
> thing; I had a look at Broag (hail Dr Drivel) for example and they don't
> appear to have installers north of Hadrian's Wall.
--
Cheers,
John.
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Kostas Kavoussanakis
> Kostas Kavoussanakis wrote:
>>
>> My very friendly installer only does the Vaillant 831 and the
>> Worcester-Bosch 30Si, and as I would prefer to use his services, I thought
>> I would investigate. If I read their specs well (I could not find much on
>> the Vaillant website) they are pretty marginal for my
>
> Try here, for full installation instructions:
>
> http://www.vaillant.co.uk/installers/heating-solutions-1/high-efficiency-boilers-2/combination/ecoTEC_plus
>
> and here for the controls:
>
> http://www.vaillant.co.uk/installers/heating-solutions-1/controls-and-diagnostics/controls-2/
Many thanks John!
>> property (3 bed detached, 2 baths, Scotland; the W-B site recommended the
>> 42CDi or the Highflow 440CDi), but let's not dwell on that.
>
> Marginal for hot water or for heating?
Well, I changed the settings of the search from 2 bathrooms to 1 plus
shower room, and it returned the 30 and 37 CDi and the 30 Si. But the
search is pretty basic:
http://www.worcester-bosch.co.uk/homeowner/products/find-a-boiler
>> Back to boilers, in terms of features, I (think) I would like weather
>> compensation, for example. Also, they both appear to modulate, but who can
>> tell how low they modulate? I also (think I) would like stainless steel
>> exchangers; have these got them?
>
> The vaillant's have SS HEs, the WB's use silicon coated ali. Modulation range
> is something like 3:1 IIRC on both (so a 24Kw unit will go down to 8kW).
The page you linked above suggests the following central heating heat
output range for the ecoTEC plus 831: 8.7 - 24.0kW. Does this mean
that the lowest it will modulate is to 8.7, or is this a different
measurement?
> I think you probably need the WB CDi range to support the posher
> controls like weather compensation - although that may only apply
> for split temperature operation with a cylinder rather than a combi)
I read and saved your post last week re added parts for W-B.
Does modulation happen anyway as a result of demand variation, or does
one need suitable room or external sensors?
Re Vaillant, is the only option for 2 zones the 358-quid Vrc 430 + Vr
61 2 Heating Zone Kit, or can I just add another zone using any stat
and a valve?
So many options, such high costs...
Cheers,
--
Kostas
John Rumm
No, that's the minimum output...
>> I think you probably need the WB CDi range to support the posher
>> controls like weather compensation - although that may only apply for
>> split temperature operation with a cylinder rather than a combi)
>
> I read and saved your post last week re added parts for W-B.
>
> Does modulation happen anyway as a result of demand variation, or does
> one need suitable room or external sensors?
No, modulation will happen anyway. Without a weather compensator, the
boiler will maintain a set flow temperature, and also possibly attempt
to maximise condensing efficiency by keeping the return temperature
lower if it can. So as the return temp creeps up it modulates the power
down.
> Re Vaillant, is the only option for 2 zones the 358-quid Vrc 430 + Vr 61
> 2 Heating Zone Kit, or can I just add another zone using any stat and a
> valve?
The VR430 is usually about �100, and the VR61 about �70. There are quite
number of ways the above beasties can be configured, for multiple zones
- some offering temperature mixing for things like UFH. You could (I
expect - not read through in detail) do a bog standard S+ plan system
with ordinary stats and zone valves for a fixed flow temperature all
over. Or you could go for the weather compensated version and have two
zones running with compensation - there is another add on control to go
with the VRC430 if you want fully temperature sensing stat on the second
zone.
> So many options, such high costs...
Costs are not so bad if you shop about a bit.
http://www.plumbnation.co.uk/site/vaillant-vrc430-digital-weather-compensator-0020028520/
http://www.vhsdirect.co.uk/product/vr_61_mixer_module/
YAPH
> Importantly, how reliable are these? I understand they are pretty
> popular brands, so spares are unlikely to be a problem. And that's a
> big thing; I had a look at Broag (hail Dr Drivel) for example and they
> don't appear to have installers north of Hadrian's Wall.
Both types are probably pretty reliable. I've been fitting W-Bs for a
while and only know of one, predecessor of the current ranges, that's
given problems with the boiler itself (if you Google back a few weeks
there's also an issue with Y-plan controls which AIUI may not be confined
to W-B). I've had 2 or 3 Vaillants (only one of which I fitted: the only
one I've fitted) that have had problems ranging from howling noises when
running at full bore to leaking heat exchanger seals.
W-B's tech support is not always 100% on the ball with the more obscure
problems (such as the Y-plan issue) but at least they answer the phone.
Vaillant's are, IME, a complete waste of time. They actually suggested it
was better to email them and they'd call me back (which to be fair they
did, but that's not much help when it's next day and the customer's still
without heating in the middle of winter).
--
John Stumbles -- http://yaph.co.uk
Eagles may soar, but weasels don't get sucked into jet engines.
Kostas Kavoussanakis
> Kostas Kavoussanakis wrote:
>> On Wed, 28 Oct 2009, John Rumm wrote:
>>
>> Does modulation happen anyway as a result of demand variation, or
>> does one need suitable room or external sensors?
>
> No, modulation will happen anyway. Without a weather compensator,
> the boiler will maintain a set flow temperature, and also possibly
> attempt to maximise condensing efficiency by keeping the return
> temperature lower if it can. So as the return temp creeps up it
> modulates the power down.
Thanks. So (having read the other thread, where it was claimed that,
for the W-B at least, there is no real gain for domestic
applications) is there no particular gain or timely return of
investment from using the modulating thermostats and weather sensors?
Judging (from an ignorant POV) by the wiring diagrams of the VR61,
it could be quite a task to set this all up.
>> Re Vaillant, is the only option for 2 zones the 358-quid Vrc 430 +
>> Vr 61 2 Heating Zone Kit, or can I just add another zone using any
>> stat and a valve?
>
> The VR430 is usually about £100, and the VR61 about £70. There are
> quite number of ways the above beasties can be configured, for
> multiple zones - some offering temperature mixing for things like
> UFH. You could (I expect - not read through in detail) do a bog
> standard S+ plan system with ordinary stats and zone valves for a
> fixed flow temperature all over.
What does "fixed flow temperature" mean in this instance? I could
perhaps desire to not heat a zone too much in the mornings, but heat
it more in the afternoon; is that out of scope?
>> So many options, such high costs...
>
> Costs are not so bad if you shop about a bit.
>
> http://www.plumbnation.co.uk/site/vaillant-vrc430-digital-weather-compensator-0020028520/
> http://www.vhsdirect.co.uk/product/vr_61_mixer_module/
Thanks, I had seen that, but in browsing the literature it seemed to
me that you need more that a 430, a 61 and a 81 for two zones (and was
thus attracted to the kit). I guess I was wrong. Meanwhile, the CM907
is 50-55 quid.
Cheers,
--
Kostas
Kostas Kavoussanakis
This is all extremely useful, esp. as, if I can afford it, I would
also like to move the boiler in the (unfloored) loft.
I should say that Broag (Remeha) emailed me back within a day with the
details of a local installer that does their range.
It will be interesting when the time comes for me. I think the
challenge is to find a recommended fitter who supports the improved
controls and features (and even more basic things, like combi vs
system), while offering a personal service. In the meanwhile I will
keep collecting information.
Many thanks!
--
Kostas
John Rumm
> On Thu, 29 Oct 2009, John Rumm wrote:
>
>> Kostas Kavoussanakis wrote:
>>> On Wed, 28 Oct 2009, John Rumm wrote:
>>>
>>> Does modulation happen anyway as a result of demand variation, or
>>> does one need suitable room or external sensors?
>>
>> No, modulation will happen anyway. Without a weather compensator, the
>> boiler will maintain a set flow temperature, and also possibly attempt
>> to maximise condensing efficiency by keeping the return temperature
>> lower if it can. So as the return temp creeps up it modulates the
>> power down.
>
> Thanks. So (having read the other thread, where it was claimed that, for
> the W-B at least, there is no real gain for domestic applications) is
> there no particular gain or timely return of investment from using the
> modulating thermostats and weather sensors? Judging (from an ignorant
You mean for having weather compensation? My guestimate is it might
reduce the gas bill by about 10% - some gain from extracting a few %
more condensing efficiency from the boiler, and the remainder from
maintaining better temperature control with fewer overshoots in
temperature. So you can translate that into money and payback time based
on your bills. In my case its worth having, since it will payback fairly
quickly.
> POV) by the wiring diagrams of the VR61, it could be quite a task to set
> this all up.
To an extent its a simple or as complex as you want to make it. You
could go for complexity not much dissimilar from a normal S or Y plan
system without any need for blended temperatures. Let the weather
compensator set a flow temperature for the whole house based on
conditions and then have conventional zones that all run at that
temperature.
>>> Re Vaillant, is the only option for 2 zones the 358-quid Vrc 430 + Vr
>>> 61 2 Heating Zone Kit, or can I just add another zone using any stat
>>> and a valve?
>>
>> The VR430 is usually about �100, and the VR61 about �70. There are
>> quite number of ways the above beasties can be configured, for
>> multiple zones - some offering temperature mixing for things like UFH.
>> You could (I expect - not read through in detail) do a bog standard S+
>> plan system with ordinary stats and zone valves for a fixed flow
>> temperature all over.
>
> What does "fixed flow temperature" mean in this instance? I could
With a "normal" install you set the boiler flow temperature with a knob
on the front. It then generates water with that as a target flow
temperature. (apart from when recharging a hot water cylinder where it
may run hotter). If you set the temperature high then you reduce the
boiler efficiency, if you set it low then you may not get the house warm
enough on cold days. This would lead to a certain amount of manual
intervention to get best performance from the system. The weather
compensator automates this, by dropping the temperature to the minimum
necessary to heat the place, it also feeds control to the boiler based
on actual temperature data rather than just "on" or "off" requests.
> perhaps desire to not heat a zone too much in the mornings, but heat it
> more in the afternoon; is that out of scope?
No, that falls into the scope of what a prog stat (and by extension the
weather controller does anyway).
Where is gets more complicated is when you want say a flow of water at
60 ish for a rad zone, plus say 50 for an UFH one at the same time. The
boiler can only produce water at one temperature (even if the weather
comp has final say as to what temperature that actually is). Here you
need a blended circuit, with a variable mixer and sensors that can run
the cooler zone using some primary flow water mixed with some cooler
return water to keep that zone working at a lower temp. The VR61 will
also let you do that (in combination with the right valves) if you want.
>>> So many options, such high costs...
>>
>> Costs are not so bad if you shop about a bit.
>>
>> http://www.plumbnation.co.uk/site/vaillant-vrc430-digital-weather-compensator-0020028520/
>>
>> http://www.vhsdirect.co.uk/product/vr_61_mixer_module/
>
> Thanks, I had seen that, but in browsing the literature it seemed to me
> that you need more that a 430, a 61 and a 81 for two zones (and was thus
> attracted to the kit). I guess I was wrong. Meanwhile, the CM907 is
> 50-55 quid.
You need "more" in that you also need the zone valves. I don't think you
need any extra electronic kit (the external sensor for the 430 comes
with it, and a cylinder sensor comes with the VR61)
Kostas Kavoussanakis
> Kostas Kavoussanakis wrote:
>> On Thu, 29 Oct 2009, John Rumm wrote:
>>
>>> Kostas Kavoussanakis wrote:
>>
>> Thanks. So (having read the other thread, where it was claimed that, for
>> the W-B at least, there is no real gain for domestic applications) is there
>> no particular gain or timely return of investment from using the modulating
>> thermostats and weather sensors? Judging (from an ignorant
>
> You mean for having weather compensation? My guestimate is it might reduce
> the gas bill by about 10% - some gain from extracting a few % more condensing
> efficiency from the boiler, and the remainder from maintaining better
> temperature control with fewer overshoots in temperature. So you can
> translate that into money and payback time based on your bills. In my case
> its worth having, since it will payback fairly quickly.
How much of this can one get with a (programmable), decent, digital
room-stat, like the CM907? I mean, do you get better temp control and
fewer overshoots with the modulating room stats?
>>>> Re Vaillant, is the only option for 2 zones the 358-quid Vrc 430 + Vr 61
>>>> 2 Heating Zone Kit, or can I just add another zone using any stat and a
>>>> valve?
>>>
>>> The VR430 is usually about £100, and the VR61 about £70. There are quite
>>> number of ways the above beasties can be configured, for multiple zones -
>>> some offering temperature mixing for things like UFH. You could (I expect
>>> - not read through in detail) do a bog standard S+ plan system with
>>> ordinary stats and zone valves for a fixed flow temperature all over.
>>
>> What does "fixed flow temperature" mean in this instance? I could
>
> With a "normal" install you set the boiler flow temperature with a knob on
> the front. It then generates water with that as a target flow temperature.
> (apart from when recharging a hot water cylinder where it may run hotter). If
> you set the temperature high then you reduce the boiler efficiency, if you
> set it low then you may not get the house warm enough on cold days.
Is this correct even in modulating boilers (w/o external or modulating
temp sensors)?
> Where is gets more complicated is when you want say a flow of water at 60 ish
> for a rad zone, plus say 50 for an UFH one at the same time. The boiler can
> only produce water at one temperature (even if the weather comp has final say
> as to what temperature that actually is). Here you need a blended circuit,
> with a variable mixer and sensors that can run the cooler zone using some
> primary flow water mixed with some cooler return water to keep that zone
> working at a lower temp. The VR61 will also let you do that (in combination
> with the right valves) if you want.
Two things to say here:
- Thanks!
- Wow!!!
(probably out of my scope this, but way cool).
>>> Costs are not so bad if you shop about a bit.
>>>
>>> http://www.plumbnation.co.uk/site/vaillant-vrc430-digital-weather-compensator-0020028520/
>>> http://www.vhsdirect.co.uk/product/vr_61_mixer_module/
>>
>> Thanks, I had seen that, but in browsing the literature it seemed to me
>> that you need more that a 430, a 61 and a 81 for two zones (and was thus
>> attracted to the kit). I guess I was wrong. Meanwhile, the CM907 is 50-55
>> quid.
>
> You need "more" in that you also need the zone valves. I don't think you need
> any extra electronic kit (the external sensor for the 430 comes with it, and
> a cylinder sensor comes with the VR61)
Ah, thanks for this. Yes, the extra valve is unavoidable for the zone
(and I guess one can use any valve, rather than a Vaillant own
thing?).
This has all been very enlightening, many thanks.
--
Kostas
John Rumm
>> You mean for having weather compensation? My guestimate is it might
>> reduce the gas bill by about 10% - some gain from extracting a few %
>> more condensing efficiency from the boiler, and the remainder from
>> maintaining better temperature control with fewer overshoots in
>> temperature. So you can translate that into money and payback time
>> based on your bills. In my case its worth having, since it will
>> payback fairly quickly.
>
> How much of this can one get with a (programmable), decent, digital
> room-stat, like the CM907? I mean, do you get better temp control and
> fewer overshoots with the modulating room stats?
In general the digital stats are usually a little better than the
mechanical ones, however they are all feedback based systems ultimately.
Some of them "learn" the characteristics of the house (so called
optimising stats) and attempt to anticipate when to turn on an off based
on assumptions derived from past data.
A weather compensator is fundamentally different in that it is partly a
feed forward system, and also offers proportional control. The feed
forward aspect is that it takes account of the actual outside
temperature as an input parameter. It then also has an addition user
selected input which is the response curve (you choose this match the
type of construction of the house - steeper curves are used for
properties with poorer insulation). In operation, it also is not limited
to "run" / "don't run" control, but instead can demand "run at 53
degrees flow" or 60 degrees flow etc. The demanded temperature can
change dynamically to match the heat loss curve and also the outside
temperature. So during the space of a day you would expect it to sweep
the flow temperature over a range of values to maintain a comfortable
environment in the house. Hopefully this variation of demand should
track the heat losses such that the temperature does not overshoot, and
you save some energy that would normally be lost heating the place to
above the required temperature. Because the compensator is using the
"right" flow temperature at all times, then the boiler should be running
at the best condensing efficiency it can in the circumstances.
>>> What does "fixed flow temperature" mean in this instance? I could
>>
>> With a "normal" install you set the boiler flow temperature with a
>> knob on the front. It then generates water with that as a target flow
>> temperature. (apart from when recharging a hot water cylinder where it
>> may run hotter). If you set the temperature high then you reduce the
>> boiler efficiency, if you set it low then you may not get the house
>> warm enough on cold days.
>
> Is this correct even in modulating boilers (w/o external or modulating
> temp sensors)?
Yup generally. The modulation will vary the input power to prevent the
set point temperature being exceeded - some may also optimise the return
temperature for better efficiency. Most people will set the flow
temperature to be "enough" to cope with most days, then perhaps tweak it
up on cold ones.
(with older non condensing boilers, conventional wisdom was to leave the
boiler state set to a high value to ensure the return temperature was
above the dew point as much as possible. Thus preventing condensing as
much as possible - since this would corrode the HE rapidly)
>
>> Where is gets more complicated is when you want say a flow of water at
>> 60 ish for a rad zone, plus say 50 for an UFH one at the same time.
>> The boiler can only produce water at one temperature (even if the
>> weather comp has final say as to what temperature that actually is).
>> Here you need a blended circuit, with a variable mixer and sensors
>> that can run the cooler zone using some primary flow water mixed with
>> some cooler return water to keep that zone working at a lower temp.
>> The VR61 will also let you do that (in combination with the right
>> valves) if you want.
>
> Two things to say here:
>
> - Thanks!
> - Wow!!!
>
> (probably out of my scope this, but way cool).
Don't take all of this a gospel on the internal operation of the
Vailliant - I don't have visibility of their algorithms, and can only
base this stuff on standard control theory and what they publish. The
general thrust ought to be about right - the actual detail of how
control is achieved can vary.
>>> Thanks, I had seen that, but in browsing the literature it seemed to
>>> me that you need more that a 430, a 61 and a 81 for two zones (and
>>> was thus attracted to the kit). I guess I was wrong. Meanwhile, the
>>> CM907 is 50-55 quid.
>>
>> You need "more" in that you also need the zone valves. I don't think
>> you need any extra electronic kit (the external sensor for the 430
>> comes with it, and a cylinder sensor comes with the VR61)
>
> Ah, thanks for this. Yes, the extra valve is unavoidable for the zone
> (and I guess one can use any valve, rather than a Vaillant own thing?).
Yup off the shelf valves etc should be fine.
> This has all been very enlightening, many thanks.
--