Worcester 37 CDI versus Vaillant Ecotec Plus 837/937

[tonybhoy]

The WB 37 CDI pre-heat delivers near instant hot water to at obviously a reduced flow rate than the valiant but hot water is excellent on that boiler as is customer service from WB which is about the best there is out there right now.

Tony.

 

[bengasman]

The 937 is a storage combi which gives a two minute boosted flow rate whioch many consider a good idea but it costs more!

The tanks give 10 minutes of boosted DHW and take 2 minutes to re-heat.

Not at a 35 degree rise, maybe at 30 it will just about manage. The filling of the tank will only happen if there is no hot water used at all. The figures are like the fuel use of cars; you never average what it says in the book.

 

[wanleg]

The tanks give 10 minutes of boosted DHW

Sorry I'm lost, how is this possible? the tanks are a combined 15l and I presume once empty will only refill once the HW is not being used ?

The design of the 937 gives you the potential for drawing off 200 litres in 10 mins.

How you draw it off is up to you, and once the heatstore is depleted completely only two minutes later it is ready for the next 200 litres.

Sorry I'm confused by this as well. Probably me not knowing how the 937 works but I would have thought you'd get the 15l in as quick a time as it takes to get to the draw off then it would be the boilers max. of 15l per min after that. Is the boiler capable of delivering 15l per min HW flow AND recharging the 15l tank at the same time ?


BTW I measured my incoming mains at just under 16l per min.

 

[tonybhoy]

BTW I measured my incoming mains at just under 16l per min.

Well you can forget any of the above boilers, you'll have to consider a WB 30CDI or similar output boiler.

Tony.

 

[simond]

Sorry I'm confused by this as well. Probably me not knowing how the 937 works but I would have thought you'd get the 15l in as quick a time as it takes to get to the draw off then it would be the boilers max. of 15l per min after that. Is the boiler capable of delivering 15l per min HW flow AND recharging the 15l tank at the same time ?

The 15litres is kept hotter and is blended with the real time output of the boiler to achieve the better performance.

But as my learned friend has pointed out, if you only have 16 l/m then you'd be wasting your money with this boiler.

 

[mickyg]

Not at a 35 degree rise

yes at 35c delta T. 15.2l/min 200litres.

 

[bengasman]

yes at 35c delta T. 15.2l/min 200litres.

Will stick my hands up in advance and confess that maths have always been my weakest side of the sciences, but it still seems to me that the marketing boys have been doing clever things with the figures.

20 l/min @ 35 increase for 10 minutes makes 200 litres.
"Burner" capacity 15 l/min
Storage tank 15 litres makes 1.5 l/min.

How do you mix 1.5 litres of hot water with 3.5 litres of cold water to end up with a 35 degree increase of the total 5 litres?
You would need water of 2.3 X 35 degrees hotter than the incoming, i.e. 85C in winter and 95C in summer, or thereabouts.

Could it be that it is not a combined 15 litres, but each tank 15 Litres? That would work; the water stored would only have to be about 60C.

To OP, have you checked that your stopcock in the house and the streetvalve are both fully open?

 

[mickyg]

not quite sure of the maths but I've tested a new one and it does what it says on the tin. Personally I prefer the GW Ultrapower but thats another story.
I've got a nice graphic in flash player for the aquaplus which works in the same way if your interested.

 

[bengasman]

Why not? Can you stick it on here with a link? If not, emailythingy will do the tricky.

 

[mickyg]

tried putting it up but cos it uses flash player or the like it won't work. I'll send it.

 

[bengasman]

Nice demo, will have a look one of these days at the technical drawings and see if I can work out how the mixing dufa adjusts to a flow between 15 and 20 litres.

 

[wanleg]

To OP, have you checked that your stopcock in the house and the streetvalve are both fully open?

In the house I believe so, street valve no idea. Is 16 litres per min considered poor ?

Forgive my ignorance but why isn't 16 litres per min mains flow suitable for a boiler that gives out just over 15 litres per min of DHW

Maybe my testing was flawed....I currently have no kitchen due to extension...the incoming mains has a tee...one end goes upstairs the other has an outside tap attached for builders to use....I measured flow with a small length of hose connected to outside tap and 2 litre bottle. Took a bit under 8 seconds to fill bottle.

 

[bengasman]

16 l/min is fine for a boiler that gives 15l/min, as long as nobody else in the house uses any water.
On the whole, 16 l/min is not impressive.

 

[wanleg]

This may have restricted flow ever so

View media item 14667

 

[mickyg]

This may have restricted flow ever so

View media item 14667

not as much as your boiler will.