Vaillant ecoTEC 415 / 615 differences and benefits?

[Mathew Newton]

I'm looking at eventually replacing my Ideal Icos heat-only boiler which currently supplies a sealed S-plan system with an unvented HW cylinder. It works well, or at least as well as an Icos-driven system can, but I know that beast isn't going to last forever. I am therefore considering one of Vaillant's ecoTEC offerings, primarily for expected benefits of the brand, weather compensation and low(er) modulation capability.

Confusingly, the Vaillant ecoTEC 415[1] is described as an 'open vent' boiler, however digging deeper it seems to be equally suitable for both open vent and sealed systems. Hence, I'd prefer to call it a 'heat only' boiler - but why don't Vaillant?

I perceive some benefits in keeping a heat only boiler, particularly with regards to spreading the components around so as not to put all my eggs in one basket. The way I see it I have far more flexibility and ease of repair by having the pump, expansion vessel, PRV and zone valves outside of the boiler. Having previously owned a combi in my old house, whose repairs was tantamount to open-heart surgery, the central heating in this new house is something of a joy to maintain given it is all spread out.

However, does anyone know what am I missing out on by considering the

415 rather than the 615[2] system boiler? Are there advantages with having the aforementioned components inside the boiler? Are the 415 and 615 otherwise essentially the same boiler, save for the location of these additional components? There's a ~=A3100 price differential but if there's a consequential functionality/capability cost of making that financial saving I'm keen to know what it is.

Regards,

Mathew

[1] 415: 615:

[newshound]

[2] 615:

have pressurised rads so never needed to consider the 400 series when replacing my combi with a system. My only comment on my new plus 637 is that there is plenty of room around the internals, especially compared to a combi. Admittedly this has a bigger "frame" than the 615. I actually have an extra expansion vessel outside, and a magnatech oxide trap, but it still makes a fairly compact package, and is neater than it would be with an external pump. I would say from my observations on build quality and design for installation and maintenance that a Vaillant is an excellent choice.

[Mathew Newton]

Bad grammar there - to clarify I've got a sealed S-plan system with an unvented HW cylinder - the only thing I'm looking at replacing is the boiler itself (and removing the pump/vessel/PRV if I go for the system boiler option).

Mathew