Storage combi - how do they actually work?

[lubemonkey]

Hi all,
Soon to get a replacement boiler and have been looking at the possibility of a storage combi (Veismann Vitodens 111 etc). Just finding it hard to get info on how they actually work.
I understand how a combi works and how a boiler with storage works. I get that the storage combi combines the two in one box, but I'm failing to read anywhere that says how it actually operates.
As a two person household a combi would work well but I like the idea of being able to have the shower running while the dishes get washed too (without putting the dishes in the shower tray).
I don't like timed hot water storage that we may not use or we have to wait on because we don't know when we want it.
Say the storage combi boiler has been inactive for a couple of days and I open the hot tap what actually happens in the boiler and tank?
Is it heating more water than I need if I'm just washing my hands?
Is there a timer involved at all?
Is there an option to have it run like a straight combi when multi outlet hot water is not needed?
I'm just trying to find out where my gas dollar would actually be spent.
Any clarity on this much appreciated.

 

[Gasguru]

Viessmann are rare boilers, unnecessarily over complex and much overrated...pioneering design where the customers are used as the test bed.
When the warranty doesn't cover the repair the parts are extortionate and few merchants stock them.

Storage combis are less reliable than normal combis..more parts to go wrong.

You need to check the flowrate versus pressure before deciding what route to go down.

Storage combis just store heated water ie. they have a reserve of heat energy. Once the store is depleted they revert to a standard combi output.
There are plenty of combis without storage will provide sufficient hot water to run a couple of outlets...the new Worcester range goes up to 50kW AFAIR...that's equal to having 2 old base model combis.

The savings between all the options are negligable...the manufacturers (especially those predominantly producing combis) along with corrupted energy organisations have tried
to make out that combis are much more efficient...it simply isn't the case. Any slight heat loss from a modern cylinder contributes to the space heating for 7 months of the year, and for the
rest of the year is offset by the significant cycling losses of a combi each time the hot tap is used.

My own dedicated 12kW boiler feeds an unvented cylinder...it burns in a single cycle, you can't get more efficient than that.

 

[JohnD]

Viessmann are rare boilers

?

How many boilers do you think Viessmann make in a year?

What do you think these people are doing?

And what's this?

 

[lubemonkey]

Thanks for the reply but


"Storage combis just store heated water ie. they have a reserve of heat energy. Once the store is depleted they revert to a standard combi output"

My question is how is that achieved? If I demand nothing from the boiler is it constantly heating this "store" in the background?
I just want to know the actual process of how they work.

 

[Gasguru]

?

How many boilers do you think Viessmann make in a year?

What do you think these people are doing?

And what's this?

So what? VW/Audi are the largest car manufacturer but they're cars suck with design faults. They're masters of propaganda.
When you've seen as many Viessmans as I have you get the picture...even my merchants (who were supposed to be a showcase) had enough of them.
Vaillant aren't much better.
Why add the complexities of databus control for the pump and fan when no other manufacturers deems it necessary?
Why add air flow measurement when few other manufacturers bother?
Why add variable combustion control when the gas is strictly controlled in the UK?
Phone around and see how many installers even want to work on Viessmans...
Pointless technology that's not necessary at the moment.

When will people understand Germany make over complex, unreliable poducts especially at the higher end of the market.

 

[lubemonkey]

This isn't quite going as expected.
If this were an automotive forum and I asked how a diesel engine worked I've so far got:
"The pistons go up and down"
and
"German cars are rubbish"
Lol

 

[denso13]

If I demand nothing from the boiler is it constantly heating this "store" in the background?

Yes, that's the plan.

 

[Gasguru]

This isn't quite going as expected.
If this were an automotive forum and I asked how a diesel engine worked I've so far got:
"The pistons go up and down"
and
"German cars are rubbish"
Lol

You asked for advice and you got it...if you don't like the answers or don't understand...
Have you downloaded the manual and taken a look at the hydraulic diagram?
You can't magic hot water from thin air...the energy is stored and rapidly depleted giving you a higher than normal flowrate for a limited time.
I personally would never recommend a storage combi..for the extra expense they are poor value.
If I criticise your choice of boiler it is for good reason....most installers only install and have little regard for the installation or customer from then on,
I'm merely highlighting that backup and repair costs can be expensive if your warranty isn't watertight, and many warranties are voided.

 

[flameport]

Viessmann boiler instructions suggest the electrical supply to it is protected with a Type B RCD.

Your house does not have one of those. To install one, expect to pay £500.

 

[denso13]

Viessmann boiler instructions suggest

Is a recommendation compulsory?

 

[JohnD]

Viessmann boiler instructions suggest the electrical supply to it is protected with a Type B RCD.

that's odd

"Type B
Electric vehicle chargers, PV supplies."

"Type B
Three phase electronic equipment
Inverters for speed control, ups, EV charging where DC fault current is >6mA, PV"


why?

 

[ianmcd]

I wouldnt recommend a Viessmann boiler, I see a fair few and dread having to turn the power off to work on them, the pcbs are so flaky and so expensive, far too many variations, just best to avoid , far better boilers out there for the same money

 

[Bodd]

I don't see much point in these unless they can incorporate a secondary return and a back up immersion heater.

 

[flameport]

Inverters for speed control,

Most likely speed control of the pump, fan and whatever else it's got.

Is a recommendation compulsory?

No - but if their boiler produces residual current that requires a Type B, not fitting one will create a pile of other problems, including the very commonly used Type AC RCDs not working properly or at all.

If a Type B RCD is to be fitted, it can't be installed on a circuit with a Type AC already on it either.

 

[muggles]

Hi all,
Soon to get a replacement boiler and have been looking at the possibility of a storage combi (Veismann Vitodens 111 etc). Just finding it hard to get info on how they actually work.
I understand how a combi works and how a boiler with storage works. I get that the storage combi combines the two in one box, but I'm failing to read anywhere that says how it actually operates.
As a two person household a combi would work well but I like the idea of being able to have the shower running while the dishes get washed too (without putting the dishes in the shower tray).
I don't like timed hot water storage that we may not use or we have to wait on because we don't know when we want it.
Say the storage combi boiler has been inactive for a couple of days and I open the hot tap what actually happens in the boiler and tank?
Is it heating more water than I need if I'm just washing my hands?
Is there a timer involved at all?
Is there an option to have it run like a straight combi when multi outlet hot water is not needed?
I'm just trying to find out where my gas dollar would actually be spent.
Any clarity on this much appreciated.

At the risk of dragging this thread back around to the original post...

Yes, a storage combi keeps a store of water hot at all times, and uses this to boost the boiler's output. As soon as the hot tap is opened, the boiler fires up to replenish the store, but if the flow rate exceeds the rate at which the store can be reheated, the store will eventually run out and either the temperature of the water coming out the taps reduces, or the flow rate reduces (usually the former). The degree of control you have over the heating of the stored water will vary from boiler to boiler.

If you've got space, the Combi Superflow coupled to an Intergas boiler might well suit your requirements. The level of control you seek is available with this, and it'll give you great flow rates when you need them.