Vaillant Ecotec plus 831 strong enough

[psarinuk]

Hi?
I've a 3 bed terrace house that has been extended downstairs.
Have a jaccuzi bath and column shower enclosure upstairs and a wetroom with normal shower downstairs.
Currently we have an old boiler with copper tank for DHW. The DHW is pumped and works really well for jacuzzi and other 2 showers along with a balancing valve for Cold water mixing.
Now we want to go for a Vaillant combi boiler, been suggested that 831 ecotec plus is good for us. I've tentatively agreed but now seem some other bigger ones online like the 838.
Could someone please suggest if 831 is adequate for my DHW needs or should I go for something bigger?
Thanks all.

 

[bernardgreen]

2 showers

Now we want to go for a Vaillant combi boiler

These quotes tend to contradict each other, combi's are not best when there are two showers. or even a shower and a hot tap in the kitchen

Keep the hot water cylinder, then you can have two showers running at the same time.

 

[psarinuk]

Sorry I should have mentioned that we only want to run one shower/ bath at a time.

 

[eveares]

If you do go for a combi/storage combi, you may want to set the water temp high and then use a mixer to lower the temperature thus improving HW flow rate.

 

[psarinuk]

: If you do go for a combi/storage combi.

Which combi: Vaillant 831 or 838?

 

[eveares]

I personally have a Vaillant ecoTech Plus 937 what is a storage combi boiler with a 14L HW tank built in what I believe is the predecessor to the ecoTech Plus 938.

If you can afford the ecoTEC Plus combination 938 and have got room for it (It's 600mm Deep) then that is what I would personally recommend. It can be picked up online for around £1,500.

https://www.mrcentralheating.co.uk/vaillant-ecotec-plus-938-combi-storage-boiler-easy-pick-pack

 

[AGAS]

If you can afford the ecoTEC Plus combination 938 and have got room for it (It's 600mm Deep) then that is what I would personally recommend. It can be picked up online for around £1,500.

really ?

 

[Agile]

Amazing that so many people can believe that any combi can be better than an unvented cylinder !

Or that you can blindly fit a combi without measuring the dynamic flow rate from your mains supply.

Looks like you are heading for a disappointment.

 

[eveares]

really ?

For a Vaillant Combi, Yes. Not saying that a combi is the only or best option, just that if it has to be a combi, then I would chose the ecoTech Plus 938.

 

[DP]

really ?

For a Vaillant Combi, Yes. Not saying that a combi is the only or best option, just that if it has to be a combi, then I would chose the ecoTech Plus 938.

What if after you have installed such a boiler that has say 18l per minute hot water delivery, your mains can only deliver 12l per minute, who is in gif major disappointment

 

[eveares]

you have installed such a boiler that has say 18l per minute hot water delivery, your mains can only deliver 12l per minute

Your HW flow rate is never going to be greater than the incoming mains flow rate for mains driven HW systems like Combi's and Unvented HW Cylinders. To exceed the mains flow rate, as pumping directly from the mains is not normally permitted, surely you would have to pump a gravity fed HW system.

 

[Bunnyman]

I think agas knows that as he a very experienced plumber eveares, I think he was playing devils advocate.... Many come on this forum buy the biggest output they can (938) and wonder why they only get 10 litres a min out,,, because nobody thought to measure the incoming main ...it's very common with the diy people

 

[Dan Robinson]

I would chose the ecoTech Plus 938.

Why?

 

[AGAS]

For a Vaillant Combi, Yes. Not saying that a combi is the only or best option, just that if it has to be a combi, then I would chose the ecoTech Plus 938.

basics first mate , a lot of money to spend if not suitable

 

[eveares]

I will rephrase, I would chose the ecoTech Plus 938 where a Combi is best suited for the situation and that you have sufficient incoming flow rate to achieve the 15.9 LPM DHW flowrate at 35°C temperature rise. Again, this is only my personal opinion.