viessmann 050-w and viessmann generally

[Deleted member 131795]

hello!

while saving up for a new plumbing and heating installation for my new one bedroom flat, i did a lot of research on different boilers and systems, sought some advice, and settled on a viessmann vitodens 050-w, seems to offer a lot in terms of features and reliability, offers good value etc.

researched the weather compensation thing and this is definitely the route i'd like to go. however, a viessmann installer that quoted me yesterday said the 050-w doesn't have a timer function. i couldn't believe this would be possible on a £1k boiler, so checked with viessmann and right enough, it is not included on this model; i would need a 100-w to get timer functionality!

this annoys me for a number of reasons, mostly because a simple timer is a software function that cost viessmann nothing and it probably cost them more to disable the function at the design stage; i think this is a case of simply hampering basic functionality at the low end to make the next model up seem more desirable. you might say, well, that's business. but also, viessmann push weather compensation, it's kind of what they are all about, and this itself is part of a move away from room thermostats, trvs, on / off controls etc, yet viessmann say that to get a timer i'd need a third party control. viessmann don't even make a control that is compatible with the 050-w that has opentherm, so it would need to be an eph or similar.

the reason i want a timer is simply to get a setback feature for night time, maybe drop it 2 or so degrees when i go to bed. i don't want to set programs or holidays or heat the flat differently at the weekend. it just seems mental that i have to get a separate timer / room thermostat to get this.

surely the one thing you want if you are using weather compensation is a setback feature?!

can anyone offer any help, opinions or thoughts on this?

thanks!

 

[Chuck]

In my opinion, weather compensation should be a supplement, not an alternative, to a programmable room thermostat. This is particularly the case in a flat where the losses through the walls/floor/ceiling will vary depending on what the occupants of the neighbouring flats are doing.

 

[Deleted member 131795]

In my opinion, weather compensation should be a supplement, not an alternative, to a programmable room thermostat. This is particularly the case in a flat where the losses through the walls/floor/ceiling will vary depending on what the occupants of the neighbouring flats are doing.

interesting, thanks. this is the view that most in the uk seem to share.

the other view, which is apparent on the european esp german forums; if you have a modulating boiler with weather comp, then you shouldn't use setback / timer / room thermostats at all. setback is for on/off systems. if you have weather comp you do not need setback, end of story. it's counterproductive to the logic of a modulating boiler. just let it modulate and leave it on 24/7.

i agree it's hard to get your head around the idea that something being on all the time, even at night when asleep, is going to be more efficient / cheaper. and there is also the fact that in these times, there is unfortunately, for most people, some guilt around consuming too much energy and 'leaving something on 24/7' is loosely synonymous with consuming too much energy.

then there's the counter-argument; our buildings are not nearly as well insulated as european apartments, we have way more heat loss, etc. but taking into account thermal mass and recovery times after setback, and having to heat the contents up again, you're apparently still no better off than just leaving on 24/7.

it's a debate that has been going on for over 15 years. i find it quite interesting. i'm likely going to just install the boiler with weather comp and no additional controls, and set and forget, maybe for the first year. see how it pans out.

 

[gmartine]

Although not strictly on/off you can set temp/timing controls with the ViCare app which you can use with the new ViCare room stat or other compatible. That'll give you adequate control for a modest further outlay.

Viessmann ViCare Wireless Thermostat (Modulating) ZK05991

Viessmann have developed the ViCare wireless thermostat to enable the ability to adjust your heating and hot water from anywhere around the world. Use the ViCare app from any smart device to ensure your home is powered with smart heating.

golita.co.uk

 

[Deleted member 131795]

Although not strictly on/off you can set temp/timing controls with the ViCare app which you can use with the new ViCare room stat or other compatible. That'll give you adequate control for a modest further outlay.

as far as i'm aware you can't set timing using the vicare app with the 050-w.

also, that room stat isn't compatible with weather compensation.

 

[gmartine]

The app and the boiler on it's own no but with addition of the smart room stat you should be able to.

As per the above discussion the stat not being compatble with WC makes sense.

 

[Desktop987456]

Even the 100-w heat only boiler doesn't have timer.

Does setback apply to heat only boiler since they are also on/off devices with modulating flame?

 

[Knappers]

I struggle a bit with this topic too.
Well insulated buildings with UFH - sure run it 24-7.
Rads by their nature are comparatively good at heating a space fairly quickly and have very little in terms of thermal mass.
Rads work best with thermostats and timers. I think a combination of weather comp and optimisation is best.
Some controllers do this but it's very difficult to find out how they all work with manufacturers being very focused on the gimmicky side of smart controls and giving very little meat on the actual heating command side of things.
I can with great confidence affirm tho that running wet radiator central heating on a timer and stat will be MUCH more efficient than running continuously, provided you have decent chunks of the day that it can be 'off', your not retired, in the house all day and running heating at 25deg.
I also believe that the efficiency gains of weather comp and optimisation are grossly understated if you factor in that a well balanced and smoothed out heating cycle should allow you to reduce the heating setpoint and maintain the same comfort level - possibly increasing efficiency an extra 10% or so.
That's what I think anyway!

 

[Deleted member 131795]

I struggle a bit with this topic too.
Well insulated buildings with UFH - sure run it 24-7.
Rads by their nature are comparatively good at heating a space fairly quickly and have very little in terms of thermal mass.
Rads work best with thermostats and timers. I think a combination of weather comp and optimisation is best.
Some controllers do this but it's very difficult to find out how they all work with manufacturers being very focused on the gimmicky side of smart controls and giving very little meat on the actual heating command side of things.
I can with great confidence affirm tho that running wet radiator central heating on a timer and stat will be MUCH more efficient than running continuously, provided you have decent chunks of the day that it can be 'off', your not retired, in the house all day and running heating at 25deg.
I also believe that the efficiency gains of weather comp and optimisation are grossly understated if you factor in that a well balanced and smoothed out heating cycle should allow you to reduce the heating setpoint and maintain the same comfort level - possibly increasing efficiency an extra 10% or so.
That's what I think anyway!

thanks for your input.

i'm struggling with it too! but from what i understand, viessmann boilers do weather compensation very well.

there is some really good discussion on heatinghelp forum, for example the following:

(i had to remove the link because links on forums are more harmful than capitalism and war)

my flat is a 1980s build, reasonably well insulated, cavity walls, full loft installation, double glazed, etc. i work from home, and don't go away for long periods of time. i like to keep the temperature around 18C all the time.

it seems, particularly in europe (i'm aware the properties there are better insulated) the always on weather compensation approach is far more prevalent. keep it comfortable. however, this doesn't really align with the uk views on the subject.

like you say, a lot of it comes down to the circumstances, and sure in many cases a timer will be required. i think the only way is to do your own tests and see what works out best over the course of a season or year. it's probably quite difficult. but i like the concept of 24/7 with no timers / controls / thermostats. it makes sense to me. certainly far better than manual control on it's own; this whole 'ooh i feel chilly, let's put the heating on' seems slightly whimsical and brit-like (stupid, ultimately) - i've been sat in a 30C room and felt the same comfort as when the room was 20C on many occasions. similarly, when using on/off controls, i've felt chilly when the temp drops slightly below the desired temperature, even though that temperature was around 19C!

surely what we want is comfort, not knee jerk adjustments that will result in comfort only a third of the time.

i get what you're saying. but i think well a well configured 24/7 weather compensated system is the way forward and, sure, it might be that it doesn't always result in an outright cheaper fuel bill, but it will be a better / more comfortable experience.

(although the germans argue it's cheaper)

 

[Knappers]

I'm pretty sure viessmann with weather comp will work well with 3rd party control but avoid anything with opentherm, you just want on/off control (with setback option at 12°C-15°C imo).
Avoid viessmann vicare stat as it won't work with that and weather comp (just one or the other)

 

[Knappers]

Personally I'm not a fan of European boilers.
British boilers work best for British situations.
Great quality boiler with great installer incentives but parts and aftercare are miles from the likes of Worcester and Baxi.
In my mind it's like buying a household appliance with a euro plug designed to work on 60hz - just not quite right for us

 

[Deleted member 131795]

I'm pretty sure viessmann with weather comp will work well with 3rd party control but avoid anything with opentherm, you just want on/off control (with setback option at 12°C-15°C imo).
Avoid viessmann vicare stat as it won't work with that and weather comp (just one or the other)

dammit i wanna go without the additional controls altogether if possible!

most installers just bundle in an EPH C4 with these, which is a decent controller. it's opentherm but you can use on/off too.

yeah, aware of the incompatibility with weather comp and that device.

 

[Deleted member 131795]

Personally I'm not a fan of European boilers.
British boilers work best for British situations.
Great quality boiler with great installer incentives but parts and aftercare are miles from the likes of Worcester and Baxi.
In my mind it's like buying a household appliance with a euro plug designed to work on 60hz - just not quite right for us

interesting perspective.

yeah, earlier in the year i looked at wb 2000 and 4000. a few weeks ago they brought out the 1000 which is their new and first ever 'budget boiler' - any thoughts on that?

from all my research the feeling i got was the they are less reliable than viessman though?

i was also quite interested in the main eco compact for a while.

 

[Knappers]

I haven't gone through the 1000 yet but I like the 4000 (not so much the 2000).
Main is a budget Baxi but with no rear piping option.
I like WB with bosch easy control on a combi with one zone.
Baxi/main with opentherm controls is another option but only have a 5:1 modulation ratio opposed to 10:1 on WB (min around 6kw vs 3kw ish on worcester) minimum matters!

With more than one piped heating zone I think the best option is probably a wired weather comp sensor and 230v switching controls with setback temp between 12&15degc (baxi do an in-flue weather comp sensor which is nice)

There's no doubt Viessmann are nice boilers but with the service network of WB if a slight difference in reliability exists, its more than compensated for!

 

[Knappers]

I've recently started to question the UV stability of some of the baxi plastics too but it's just a feeling....tbc

 

[Knappers]

This is how I see it...
If your going to compare just the boilers on their technical merit then I'd rate them:
-viessmann
-vaillant
-worcester (very close behind)
-
-baxi

Manufacturers controls:
-Worcester
-viessmann
-vaillant
-baxi

On parts availability:
-worcester/vaillant/baxi
-
-
-viessmann

Service/aftercare:
-worcester
-vaillant/baxi
-
-viessmann (Good service just small in UK)

Worcester boilers can be awkward to work on but not so much that it warrants charging extra so often not liked by engineers.

Viessmann could be great in theory with a larger market share and re-investment in our market but in reality it's not going to happen, if it did the company focus isn't going to be on UK market.

For me in situations WB works then they're the winners in terms of the best overall package for customers.
However I do specify either worcester, baxi or viessmann boilers for different jobs, depending on the situation

 

[Deleted member 131795]

I haven't gone through the 1000 yet but I like the 4000 (not so much the 2000).
Main is a budget Baxi but with no rear piping option.
I like WB with bosch easy control on a combi with one zone.
Baxi/main with opentherm controls is another option but only have a 5:1 modulation ratio opposed to 10:1 on WB (min around 6kw vs 3kw ish on worcester) minimum matters!

With more than one piped heating zone I think the best option is probably a wired weather comp sensor and 230v switching controls with setback temp between 12&15degc (baxi do an in-flue weather comp sensor which is nice)

There's no doubt Viessmann are nice boilers but with the service network of WB if a slight difference in reliability exists, its more than compensated for!

allen hart and tomkat gas training both uploaded short videos on the 1000 in the last 24 hours and both seem to like it. stainless steel heat exchanger, easily accessible parts, very light, etc. although i can't seem to find any info on the modulation.

 

[Deleted member 131795]

just called worcester tech support to ask about modulation and a few other things. very impressed with their support and knowledge. the person i spoke to was so helpful. actually making me consider worcester again now..

the 1000 only modulates to 5.2kw - i'm in a small one bedroom flat with only two rads and a heated towel rail. when i mentioned this he did suggest considering the 2000 or 4000 just because they modulate down to 4.8kw or 3kw respectively.

 

[Knappers]

I like the 4000 but it is a heavy lift.
Where is it going?
4000 won't easily fit a kitchen cupboard, 8000 is big and designed to replace a cupboard!
Worcester 1000, baxi 600/main, Vaillant ecofit
Will fit a 300mm cupboard.
I'm not aware of a 10:1 modulating boiler that will fit a 300mm cupboard but some may fit a 350mm

 

[Deleted member 131795]

initially thought kitchen but now preferring the idea of cupboard in bedroom, which is where the immersion tank is/was. it's where the cold water comes in, very central, right next to bathroom, just seems more straightforward. cupboard has big heavy door and don't think i'm going to even hear a 52db boiler, that's if it's going to ever be doing much in the night anyway.

 

[Chuck]

this whole 'ooh i feel chilly, let's put the heating on' seems slightly whimsical and brit-like (stupid, ultimately) - i've been sat in a 30C room and felt the same comfort as when the room was 20C on many occasions.

Personal 'comfort' is a function of (a) air temperature, (b) radiant temperature, (c) air flow velocity and (d) humidity. What an individual considers to be 'comfortable' depends on their (i) age, (ii) sex, (iii) activity level, (iv) clothing, (v) health and probably other factors I've forgotten.

i like the concept of 24/7 with no timers / controls / thermostats. it makes sense to me.

Plenty of schemes that seem like a nice idea in theory don't work well in practice.

In my experience, people hate not having control of their own environment. You see the effects of this in offices that have centrally controlled BMS. The occupants wedge doors/windows open, obstruct air conditioners, bring in fan heaters, etc.

 

[Knappers]

Yes, I think OP would be better off having a programmable stat and not needing it than needing it and not having

 

[Deleted member 131795]

Yes, I think OP would be better off having a programmable stat and not needing it than needing it and not having

makes sense!

 

[Deleted member 131795]

thanks for all the input. the viessmann approved engineer has quoted me £4200 for the complete job which seems reasonable.

this is to remove old immersion tank, re-route gas supply, install 050-w, two rads via attic / dropdowns, and bathroom for towel rail. install weather comp sensor, supply eph c4 room stat / programmer.

i have been toying with the idea of looking at the worcester 1000, but if you consider that the viessmann is probably the better / more reliable overall, it seems like a good option?

 

[Deleted member 131795]

knappers.. the installer suggested putting the boiler in the loft. i hadn't even thought of it. is this a good idea, in your opinion? his argument was that it would create more space in the cupboard, but i'm thinking it was probably because it's much easier to do a loft install, right? you have any thoughts on this?

 

[ShaunCorbs]

Needs to have a fixed loft ladder, light and loft boards

 

[Deleted member 131795]

was thinking about more about things like.. safety, lower operating temp affecting performance, weight on joists, the need to access the boiler quickly, etc. i dunno. i mean if there are none and all i need to worry about is a £65 loft ladder and some boards, so be it. i just thought there might be more things to consider than that.

 

[Chuck]

his argument was that it would create more space in the cupboard, but i'm thinking it was probably because it's much easier to do a loft install, right? you have any thoughts on this?

I think that if you don't trust your installer's advice and judgement you should employ someone else; if they sense your cynicism many engineers will turn down the work anyway.

Nobody I know likes putting boilers in roofs; they are dirty with difficult access and mineral wool insulation gives you skin problems. Losses from pipework will be outside the thermal envelope of the house so insulation is important as is frost protection. I see it as a last resort if there is not enough space somewhere inside the house.

 

[Deleted member 131795]

I think that if you don't trust your installer's advice and judgement you should employ someone else; if they sense your cynicism many engineers will turn down the work anyway.

Nobody I know likes putting boilers in roofs; they are dirty with difficult access and mineral wool insulation gives you skin problems. Losses from pipework will be outside the thermal envelope of the house so insulation is important as is frost protection. I see it as a last resort if there is not enough space somewhere inside the house.

interesting that you don't like putting them in roofs. he seemed to think it would be better, suggesting it would give me more space (and he has a point; it's a very small flat!) plus if it's easier for him too then great for everyone. however, my preference is the bedroom cupboard where the existing immersion tank is. i don't really need the additional space.

there is no cynicism involved i just like to understand everything, and generally ask a lot of questions.

 

[Knappers]

I would generally see loft installation as a premium installation for space saving.
It is more difficult to get to for servicing and there would be some heat losses due to the cold loft in winter.
I don't have an airing cupboard and have a system boiler and unvented cylinder in the loft.
It sounds to me like your engineer is giving good advice but if you don't particularly want the extra space then I'd stick with the cupboard.

 

[Chuck]

interesting that you don't like putting them in roofs. he seemed to think it would be better, suggesting it would give me more space (and he has a point; it's a very small flat!)

Obviously, the pro is that it would give you more space. But, that comes at the price of making access and maintenance harder, etc. As long as the installation complies with the manufacture's installation instructions you can have it wherever you like.

There's another point you should check first, however. If it's a flat, does your lease actually allow you to install a boiler in the roof? IME, it would be very unusual if that were the case. Do not assume that because the access point to the roof is in your flat that the roof space is included in your demised premises.

 

[Deleted member 131795]

yeah as mentioned i really don't have a lot of stuff so space isn't really an issue for me

it's a good point, but yes, it's my loft. it's just a block of two one up one down. i'm the freeholder too.

 

[Deleted member 131795]

I would generally see loft installation as a premium installation for space saving.
It is more difficult to get to for servicing and there would be some heat losses due to the cold loft in winter.
I don't have an airing cupboard and have a system boiler and unvented cylinder in the loft.
It sounds to me like your engineer is giving good advice but if you don't particularly want the extra space then I'd stick with the cupboard.

after taking into account some of your advice i have british gas quoting me on tuesday for a worcester bosch 4000 - just so i have another option. funnily enough british gas don't offer anything lower than the 4000 cos it's not made in uk. they consider the 4000 the entry level.

 

[ShaunCorbs]

Wouldn’t go bg

 

[Deleted member 131795]

Wouldn’t go bg

hi shaun, not the first time i have heard this.. can you elaborate?

 

[ShaunCorbs]

hi shaun, not the first time i have heard this.. can you elaborate?

There rubbish quality vs the price be ok if they were half what there quoting but not any more you might even find they will use contractors for the install so not even bg employees

 

[Deleted member 131795]

There rubbish quality vs the price be ok if they were half what there quoting but not any more you might even find they will use contractors for the install so not even bg employees

yeah.. they are certainly expensive. they quoted me £6k in feb for the 4000 and 3 rads.

i had a viessmann guy quote me last week £4k for a 050-w system.

really the attractive thing for me is mostly just the four years interest free.

 

[ShaunCorbs]

yeah.. they are certainly expensive. they quoted me £6k in feb for the 4000 and 3 rads.

i had a viessmann guy quote me last week £4k for a 050-w system.

really the attractive thing for me is mostly just the four years interest free.

Your paying at least £1k for that and also nothing is 0% just fees built in tho might be better looking for a 4 year 0% interest cc

Or a low interest cc / bank loan

 

[Knappers]

For the price BG will quote I would expect perfection. For BG money I would throw in a powerflush and be fitting the very top of the range equipment, with the most beautiful pipework and perfect balancing.
That's not what you'll be getting tho!
Support local small buisness'

 

[Deleted member 131795]

For the price BG will quote I would expect perfection. For BG money I would throw in a powerflush and be fitting the very top of the range equipment, with the most beautiful pipework and perfect balancing.
That's not what you'll be getting tho!
Support local small buisness'

Yeah I also don't like the fact they don't give you the manufacturer's warranty, instead giving you their own reduced five year one. Seems like a bit of a trick, that.

The reason I am going to get a final quote from them is because my ex partner she keeps on and on at me saying they're the best and that they might seem dearer to begin with, they aren't.. and then she will give a ton of reasons.. like she seems to think that they are the only company to to provide a fixed quote that includes everything, including all the sub contractors jobs, add ons, roof work, electrics, etc. unlike locals and independents who will charge extras if things come up that they haven't accounted for.

I don't really have enough experience of this to know if she is right or wrong, but the locals firms that quoted me all stated that their quotes included all necessary work and there would be no additional costs.

 

[Knappers]

There is some security in going for a big reputable company like BG.
They will always have someone to answer the phone for example.
As a simily its probably like booking a hotel room with a big chain like Hilton vs a private rental cottage. You know your getting much better value with the cottage but you'd expect to give some grace on returning calls and you don't know exactly what to expect untill you get there.
But your always going to get more value.

In my experience big firms like BG often use their warranty to compensate for the quality of installation. For example- they have recently reduced their one off service fee and include a years warranty. When I had a customer query why they should use me I pointed out that while BG will do a very basic service and pick up the faults as they happen, my service is designed to find the issues before they happen and prolong the overall life of the boiler.
Would you rather have the boiler break down and be repaired for free - or just not have it break down in the first place?

Also if you want boiler cover with BG then you can just pay monthly - they don't need to have installed it! (Obviously free cover with install isn't actually free)

 

[Deleted member 131795]

just had a quote from BG for full install with WB 4000

£7184.20

vs viessmann guy quoted me last week £4250 for same with 050-w

 

[Knappers]

I'd probably be able to do half that, then
If you don't like it - I'll just do it again

 

[Deleted member 131795]

I'd probably be able to do half that, then
If you don't like it - I'll just do it again

knappers

can you please advise on the following?

i've been quoted £3500 for a main eco compact install, which seems like a really good value install, and i particularly like the plumber that has offered this quote and want to use him regardless.

as well as baxi/main he also likes vaillant and quoted £4500 for the new ecotec plus 826 25kw

it's a lot of extra money for what is going to essentially do the same thing, but would i see any real world benefits by paying for this over the main? a lot of people are saying the main is outdated, doesn't modulate very low, won't be that efficient, or quiet, etc.

just so confused about what to do! £1000 is lot of money for me atm and i need to let him know today really

 

[Knappers]

Sorry I didn't see this yesterday.
Either would be fine.
The most important thing is that your happy and confident with the installer.
For me the decision would depend on the control options. The vaillant is more capable but only makes sense if those capabilities are being implemented with the right controls?
Does the vaillant quote have different controls and if so what?

The paradox with the right setup is that in theory it should be possible to have increased comfort and decreased running costs.
Even if its worth the extra it's not magic - you get what you pay for. With a boiler lasting say 15years are you in the possition to pay upfront for £70 worth of annual comfort?

 

[Deleted member 131795]

same control options essentially, just load compensation. the cheaper baxi option would just use a cheap EPH opentherm controller and the (much) more expensive vaillant option would include their sensohome controller.

the vaillant ecotec plus was recommended to me as the best non-budget option by syzmon from urban plumbers, simply because of the modulation going as low as 2.5kw. the heat loss in my flat is about 4.8kw.

the main eco compact only goes down to about 6.7kw

but i'm not sure just how important this extra wide modulation ratio is, over it resorting to on/off control when it reaches set point.

the main is just very basic, whereas the vaillant looks completely badass, has all kinds of app control and data stuff going on, it's a fair few db quieter too, and as it'll be going in airing cupboard in bedroom, not kitchen, this might be worth the extra.

no idea i'm so confused. an extra £1000 is a lot of money, i can manage it, but i wonder how much of a difference it would really make.

 

[Knappers]

I would like to think that vaillant controls would be more effective and I'm a big fan of matching boiler and controller (except baxi)
If 'main' is running with opentherm then there probably won't be much difference and if in a cupboard then looks don't matter.
The smart choice would probably be the main.
I'd probably chose the vaillant tho coz I'm just not very smart.
(I'm sure that doesn't help)

 

[bobbyt]

I would like to think that vaillant controls would be more effective and I'm a big fan of matching boiler and controller (except baxi)
If 'main' is running with opentherm then there probably won't be much difference and if in a cupboard then looks don't matter.
The smart choice would probably be the main.
I'd probably chose the vaillant tho coz I'm just not very smart.
(I'm sure that doesn't help)

Hi,
I recently had a Viessmann 050 25kw combi fitted with weather comp and EPH controller, which provides basic on/off temperatures if required. It replaced my old Baxi with hot water tank etc.
I'm using the CH for the first time this week, and must say it is really efficient. 10 deg outside and it is modulating at 10% and using about 3kwh when burner is on, and the burner isn't on all the time. Rooms at a constant temp of 20-21 deg. Really pleased with the whole set up, saving loads of gas compared to my old boiler which was only on 8-9 hours a day, and I have this one on all day and night with reduced night temperature set on controller. Just thought this might be useful info, if you haven't made your choice yet.

 

[Deleted member 131795]

glad you are happy with your system. i've decided that weather comp is over-hyped. not saying it doesn't do anything, it's just diminished returns; your savings are going to be because it's a modern condensing boiler with low flow temps. the weather comp doesn't do much in addition to that, and i assume the EPH controller is on/off mode as it can't work in opentherm mode at the same time as weather comp.

i am going with a main eco compact 25kw and eph cp4 control. i think that'll get me 95% of the way there.

have you thought about what would happen to your bills if you turned it off at night?

 

[bobbyt]

glad you are happy with your system. i've decided that weather comp is over-hyped. not saying it doesn't do anything, it's just diminished returns; your savings are going to be because it's a modern condensing boiler with low flow temps. the weather comp doesn't do much in addition to that, and i assume the EPH controller is on/off mode as it can't work in opentherm mode at the same time as weather comp.

i am going with a main eco compact 25kw and eph cp4 control. i think that'll get me 95% of the way there.

have you thought about what would happen to your bills if you turned it off at night?

Hi, ok thats good then, it didn't come on last night, my night setting was 18 deg, so obviously it wasn't required, overnight temps outside were 11 deg. during the day it used about 28kwh and the house felt really comfortable. It'll be a bit of a learning curve according to weather, can always alter the weather comp curve to suit if required. Yes you are correct, EPH is just an on/off switch.

I have done a lot of research on weather comp, and I think it will be really efficient at making the house feel comfortable at the same temperature, we are home all day most days as we are retired, so it suits our lifestyle. My house is also well insulated with the max thickness of loft insulation, and the recommendation is to keep the CH on to maintain the temperature, and to enable the system to heat the house up quicker in the morning, as if the temp is allowed to go too low, with the low flow temps (yesterday 40-43 deg), it will take longer to get back to 20 deg, which is what I have selected on the boiler. Anyway, as long as we are both happy