Viessmann Vitodens 100-W Compact boiler and pump overrun

[simond]

It is simple as the Mysteryman says.

Use a simple diverter 3 port valve and away you go.

WBIB is optional for pump overrun, but this is the open vent model only.

We recommend this boiler for all open vent applications below 26kw. It has a number of advantages over the competition;

1. No compartment ventilation needed
2. Small size
3. Heavyweight unique heat exchanger, not thin steel like the Giannoni commonly used by competitors
4. No requirement for a 22mm inlet (as per Bosch)
5. Simple weather comp if a customer desires it
6. Pump overrun cable not mandatory
7. Multiple flue options inc chimney liners
8. 5 yr parts and labour

Disadvantages;
1. Flow switch
2. Flueing a bit flimsy
3. Condense trap difficult to clean without spilling contents at the annual service
4. Casing top retaining insert clips are usually found broken if the box has been transported upwards by the merchants.

 

[MJN]

God you really don't get it, if hw is off and stat is calling it won't fire, if ch is calling and hw isn't it will fire, heating is wired so when demand on heat as long as hw is satisfied/or off on timer it will fire, when hw is called for on timer it will override heating hence hw priority,

Look at the wiring. If CH is calling and HW timer is off then the boiler's output will be passed to the cylinder until the cylinder stat is satisfied. This is not so bad on a non-weather compensated boiler because as soon as the cylinder is up to temperature it'll switch over to CH as requested. However, with weather compensation there is every chance that the cylinder stat will never be satisfied in this scenario hence CH won't function.

With respect eaton, I'm fairly confident in saying that it is you that doesn't get it.

Just because hw is off and timer but hw is cold it will stil function on heating as 3 port won't get signal to cyl stat until hw timer is on, it's a very basic wiring function, check out the Honeywell diagrams, it's really not complicated, I've done quite a few

You're right, it isn't complicated. But the standard W-plan wiring layout doesn't take cognisanse of a boiler with weather compensation fitted which is why I am serious doubting its suitability without the modifications I have suggested. You are missing the fact that if your boiler is operating in weather compensated CH mode then the cylinder stat will not get satisfied unless the HW timer is calling for heat (because that switches the boiler to full output).

You probably haven't noticed the shortcomings of the setup given that you've got your HW timed for such a long time hence the risk of the problem scenario occurring is reduced. This effectively works around the issue, but I don't want to always have a cylinder full of hot water as even though the losses might be small it is inefficient given our relatively small HW consumption.

Mathew

 

[MJN]

It is simple as the Mysteryman says.

Use a simple diverter 3 port valve and away you go.

But what about the scenario I have described when the HW timer isn't calling but CH is? Water will be pumped via the cylinder until the cylinder stat is satisfied but if running weather compensated that might never happen!

[Pros/cons]

Thanks for those - good to know.

Mathew

 

[MJN]

Is this a 4 pipe system boiler or heat only?

Heat only.

 

[MJN]

Just thinking aloud; does the w-plan setup comply with the Part L of the building regs with regards to independent time control of both heating and hot water?

With the default configuration, even if your HW timer is off you still end up heating the cylinder. Surely that goes against the spirit of the regs which are all about conserving energy hence the requirement for independent control of both time and temperature for CH and HW?

Mathew

 

[Kev F]

For gods sake, I do this for a living and have many times, either listen or do one, get a w plan and follow it, it's so bloody simple it's boring now, it works, they all do, your complicating things, how fecking hard is it to tell people nowadays, if you cant understand get someone to do it for you who can

 

[Kev F]

I'll admit I've not looked at any plan you've put up as I don't need to as the one I use ( Honeywell) works, I suggest you get a copy

 

[Agile]

I expect that is to enable it to be connected just like an old boiler which was when powered only when heat was required.

Tony

This is not correct. These boilers require a permanent live plus a switched live plus a pump live if overrun is wanted.

Yes, I appreciate that but is there a Viess vito on connecting the live feed and call for heat together and powering them when there is a call for heat?

I have seen them used that way when there is only a single cable between boiler and remote controls and customer did not want carpets/decorations disturbed ( or maybe installer was just lazy ).

If not then why not? What could go wrong? Thats the way Baxi Solos and similar units were used.

Tony

 

[MJN]

it works, they all do

Not in the circumstances I've described it won't.

Answer me one question:

If your HW timer is not calling for heat but your CH timer and stat are, what will happen? The boiler's output will be passed to the cylinder until the cylinder stat is satisfied, then it will divert to the CH circuit. So what happens if your cylinder stat is set to 60C but the boiler is only outputing at 50C because of weather compensation? How will the CH ever function?

Please tell me where I'm going wrong if you think my understanding is incorrect.

Mathew

P.S. I appreciate this is frustrating for you because you think I have got this wrong. But please do properly consider the scenario/question above because I'm sure I'm right!

 

[Kev F]

Tony it should have perm live, neutral, earth, then sw live, you can then add pump live. These really are that simple, if weather comped just use outdoor sensor straight into pcb. Then wire up as w plan on hw priority, as soon as hw on timer is off to stat satisfied it switches to weather comp on heating if there is a demand.

 

[DP]

MJN, Page 13, box C takes care of raising the temperature for HW cylinder when WC forces CH temperature down during mild weather.

Cylinder is unvented- is three port allowed?

 

[Kev F]

Ok I'll make this as simple as poss, if following the honeywell w plan

Ch timer on
Hot water off
Cyl stat on/off
Result ch

Hw timer on
Ch on
Cylind stat NOT calling
Result ch

Hw timer off
Ch on
Cylinder stat calling
Result ch

Ch timer on
Hw timer on
Cylinder stat call
Result hw

It doesn't matter if hw timers on and cyli isnt calling it wont go into coil as it will be in ch mode

Also if timers off and stat is on it will close to ch position and won't go round the coil, just try it and you'll see. Like I said not looked at your plan and can't be assed as the Honeywell works very well and on many occasions, I can't be wrong or I'd be out changing them all. The plans are so easy to follow if you look and follow them.


As an eg 3 port valve doesn't get a signal on either hw or ch until clock sends signal. Hence timer hw on but stat satisfied will go to ch not coil, as with timer off stat on it won't get the live from timer and will send into rads, that's it I'm bored now,

 

[gaswizzard]

Functional operation of the standard honeywell W plan.

With hot water prority motor valve will not switch to central heating unless cyl stat is satisfied , considering the programmer is a basic 10 channel then central heating can't be switched independantly of HW , cyl stat satisfied switches power to motor valve , as long as cyl stat is calling central heating won't get a look in.

Some W plans were fitted with a change-over switch or just configured for HW/CH priority.

 

[picasso]

View media item 43787
this is taken from a honeywell w plan pdf

its a draw back of the w plan you cant have ch without the dhw stat being satisfied, I havent looked at your changes but I cant see you getting over this problem.

 

[Kev F]

Functional operation of the standard honeywell W plan.

With hot water prority motor valve will not switch to central heating unless cyl stat is satisfied , considering the programmer is a basic 10 channel then central heating can't be switched independantly of HW , cyl stat satisfied switches power to motor valve , as long as cyl stat is calling central heating won't get a look in.

Some W plans were fitted with a change-over switch or just configured for HW/CH priority.

Viessmann sent me a wiring diagram where this happens so that you can just have weather comped heating with no hw