New Boiler - Weather Compensator?

[silversurfer1]

What would you recommend?


Making sure the old system is cleaned very very well and a magnetic filter. no new boilers like old systems much

ss

[moles]

Yes sludge is the worst thing you can have in a new boiler is the root of most of the problems. Viessmann are a nightmare I just cover service and repair don't do too much installation and get to work on every type of boiler out there. IMO Viessmann are nothing but trouble, god only knows how they came 3rd behind Vaillant and Worcester I'm genuinely surprised at that. I know they are not cheap but would never spend that when a worcester or valiant can be had for not much more. I always fit/recommend Vaillant for family and friends they have pretty much got it sorted with the new ecotec and have ironed out any problems they used to get over the last 8 or so years on the new ones.

[Alucidnation]

To be honest, i have also been looking into the Vaillant, but it appears that even their basic OV HO boiler will not allow easy control of existing valves room stats etc, unless i purchase another load of their connection/control boxes, and even then, i would have to use their own room stats as they are all ebus.

I have also been thinking of maybe a 4 pipe system boiler and do away with the external pump.

I am a bit limited with pipe layout, boiler location as its in a kitchen cupboard, (and funds), and so i am trying to make this as easy as possible.

Whichever way i go, i would really like to introduce the WC if possible.

[dirkgently]

Alucidnation said:

To be honest, i have also been looking into the Vaillant, but it appears that even their basic OV HO boiler will not allow easy control of existing valves room stats etc, unless i purchase another load of their connection/control boxes, and even then, i would have to use their own room stats as they are all ebus.

I have also been thinking of maybe a 4 pipe system boiler and do away with the external pump.

I am a bit limited with pipe layout, boiler location as its in a kitchen cupboard, (and funds), and so i am trying to make this as easy as possible.

Whichever way i go, i would really like to introduce the WC if possible.

Look at the baxi avanta range.

[Gingerbread Man]

moles said:

If you haven't already purchased the Viessmann i would have a rethink, they are not one of the most reliable boilers out there!.

Install quite a few through the company I sub to. They prefer them as no call backs. Not as much of a range as WB though.

[FiF]

Alucidnation said:

To be honest, i have also been looking into the Vaillant, but it appears that even their basic OV HO boiler will not allow easy control of existing valves room stats etc, unless i purchase another load of their connection/control boxes, and even then, i would have to use their own room stats as they are all ebus.

I have also been thinking of maybe a 4 pipe system boiler and do away with the external pump.

I am a bit limited with pipe layout, boiler location as its in a kitchen cupboard, (and funds), and so i am trying to make this as easy as possible.

Whichever way i go, i would really like to introduce the WC if possible.

We did a straight swap in on an open vent EcoTEC plus, on a Y plan.
We did have a new room stat and a new programmer, but not the Vaillant stuff.
The only thing that was needed was a pump overrun wire.
Of course we had the system cleaned out really well, and Magnaflush pllus the MagnaClean.

It's nearly a year now and first service coming up, keeping a track of consumption as we have changed gas supplier and gas consumption has been reduced by at least 30%, in reality more, but I've sort of made a rough adjustment for a milder winter.

[moles]

You don't need to fit any Vaillant controls can be wired up with any stats, clocks in fact i'd avoid Vaillant controls they are overkill and not the most user friendly. A hive, tado or nest would be better than a WC i reckon.

[Alucidnation]

Interesting you say that as I have a 3 zone system installed with a nest down stairs and up.

From trying to understand the Vaillant manual, the controls are ebus with no provision for 230v switching with a wc installed.

It's possible I have gone cross eyed and missed something as I have been studying this all weekend!

[moles]

No if using a Vaillant WC then you are stuck with it as it is all done on the ebus sorry i misread last post. :-)

[silversurfer1]

Moles is correct you dont need to use the ebus controls the Vaillants they will all wire with everyday controls nothing fancy needed.

The ebus is a nice touch if your using a vaillant cylinder as you can alter the HW on the boiler dial but as Moles said the vaillant controls are over kill

ss

[moles]

If no WC then they only have a single 240/24v switched live to work from and any stat control will work with it.

[moles]

A weather compensator as far as I can work out just brings the boiler on or off earlier/later depending on outside temps. i don't think they save you any money and a room stat works in the same way just is slower to react to the change in outside temp.

[Alucidnation]

With the Viessman, from what i understand, the heating runs 24/7 and adjusts the flow temp to the rads, through heat loss and depending on outside temp. i.e. if it gets cold outside it ups the flow temp to the rads. If there is a call for DHW, the heating shuts off and the boiler ramps up the temp to heat the water, a bit like a combi. The heating curve can also be adjusted manually via the temp dial on the boiler.

With the other systems, its appears that the WC works along side internal controls, and adjusts the flow temp according to the outside temp. However, i think this stays the same, even when demand for hot water, which means it would take forever for the water to heat up.

This is all from what i can make out from the brochures and manuals, which to be honest, are not very good from any of the manufacturers.

Edited by Alucidnation on Monday 26th May 22:51

[Alucidnation]

With the Viessman, from what i understand, the heating runs 24/7 and adjusts the flow temp to the rads, through heat loss and depending on outside temp. i.e. if it gets cold outside it ups the flow temp to the rads. If there is a call for DHW, the heating shuts off and the boiler ramps up the temp to heat the water, a bit like a combi. The heating curve can also be adjusted manually via the temp dial on the boiler.

With the other systems, its appears that the WC works along side internal controls, and adjusts the flow temp according to the outside temp. However, i think this stays the same, even when demand for hot water, which means it would take forever for the water to heat up.

This is all from what i can make out from the brochures and manuals, which to be honest, are not very good from any of the manufacturers.

Edited by Alucidnation on Monday 26th May 23:01

[moles]

But when you're cold you want the house up to temp quick and if it's mild the heating might come on but will reach temp quicker so will turn off on the normal room stat so really all it's doing is varying its output to match the outside conditions. On a vaillant you can set its kW output by pressing 2 buttons and setting it to the output you need for your house admittedly it stays there unless you adjust it but you shouldn't really ever need to. On mine I set the output of my boiler to 10kw and leave it at 52c on dial room stat on 20 and leave the hive on all day and drop it back to 18c on a night, it comes on when it needs to and a weather compensator won't change that, each house/boiler has a certain input/output and once set up shouldn't need changing I just don't see the point in them?.

[FiF]

As a matter of interest why would you set the output of the boiler lower? Unless it's not a modulating burner I suppose. My Vaillant kicks in gets the circuit up to temp quite quickly and then throttles back to about 5kw output.

[moles]

Condensing boilers are most efficient when at lower temps, 10kw is the lowest I can fix the output to but it only works if you leave the heating on all/most of the day as would take forever to warm up from scratch on a cold day, have a look in the manual a table in the back go to D0 and press i will tell you what output your ch is set to, is just a way of range rating it for different house sizes

[herewego]

There seems to be a contradiction here. Having the output T set low to maximise the condensing efficiency and having the boiler running when it shouldn't be, i.e. when heat isn't required.

If you have the output set low then I suppose the house will take longer to heat up therefore you will set the timer to come on earlier which will use more fuel than setting a higher boiler T and heating the house quicker. Does a higher boiler temperature in fact compromise the condensing efficiency?

Clearly the boiler should be off as much as possible. I don't understand this talk of running it 24/7, it doesn't make sense, nor does setting it back to 18 overnight. When we're asleep at night and when we're out for long periods the heating should be off or, if there's a risk of freezing, set back to say 5.

[Alucidnation]

I agree, however, i think the idea is that the house doesn't cool down at all with it on 24/7 as the system maintains a set temp, rather than being off for long periods, and then having to work harder to get back up to temp when required.

The WC sees the temp changes before the inside of the house does, so alters the boiler output accordingly so that the occupants don't feel the change.

Its a bit like climate in a car i guess.





Disclaimer: This is all a guess on my basic understanding and will be calling the manufacturers for specific details today.

[FiF]

I can't see the point in setting the output lower unless it's to match the output better to the demand for a small house /oversized boiler and thus avoid boiler cycling. That issue is automatically dealt with if the boiler has a fully modulating burner surely?