Current opinion about Vaillant EcoTec Plus 428?

16 Jul 2015
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United Kingdom
We are about to embark on a refurb of a 1930's brick and tile detached 4 bed house.
The kitchen is being moved and the wall where the 20 yr old boiler is sited will be going. We currently have an open system and the heating engineer is suggesting a pressurised system (250l unvented hot water cylinder in the loft with an 18l expansion vessel).
He has specified a Vaillant EcoTec Plus 428 boiler with Honeywell controllers. We are in a hard water area.
Reading about this boiler there seem to have been lots of issues with respect to cycling.
Have these problems now been resolved or is this still considered a problematic boiler?
Should we be looking at an alternative boiler?
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It is when the boiler is oversized!

Why has he specified a 28 kW boiler?

I don't know - he looked at the size of the house, the number of radiators, number of bathrooms etc and came up with this boiler as the one for us. We would like water based underfloor heating in the kitchen/diner and downstairs bathroom if we can do it so maybe that has a bearing on the boiler rating?
Zoning may be an issue think I would be looking at the approiate ebus controls from vaillant. With the vrc 470 you can djust the heat load to match cylinder for maximum efficency you need to use the VR10 on the cylinder so the boiler knows the temp of the cylinder rather than just calling for heat. Specify oversized radiators and take advantage of WEather compensation which in turn should mean a more even comfortable temp around the house. Are you really sure you want UFH?

Not sure if the new ones come with the revised logic, maybe our resident vaillant experts can advise.
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Thank you for your replies - looks like I need to ask a few more questions as to why he spec'd the boiler that he did. Did the 6 series suffer from the cycling problem or is the cycling more a function of choosing the wrong capacity of boiler in the first place?
Thanks again for your help & advice
Havent seen a 6 in action. It is all to do with the start up routine and how much heat can be dissapaited whilst the boiler fires at 80% of max load for 50 seconds. Maybe the 6 starts low and works its way up? However as long as you use the advanced controls then I do not see a problem with either as the boiler really shouldnt need to cycle ever as long as no one is silly with min flow temp. Key is the correct size primaries and pump.

Advantage on 4xx is that generic diverter valves (apart from the one on the unvented as needs to be as per MI)can be used and external pump think the turndown ratio may have been improved recently as well but would get that confirmed. 6xx no external pump or diverter valves (apart from the required one for the unvented)
Baxi Solo 2 is obsolete? Yes, as a whole boiler it is obsolete but its parts are ready available!
I would love to keep the old Baxi because it just soldiers on with regular servicing. Unfortunately the wall that it sits on will be going in the refurb and the heating engineer told us that we can't move it to a new location under current regulations.
I have been recommended to look at Main as an alternative manufacturer to consider with a good warranty for about £150. Any thoughts?
Nothing wrong with the vaillant, especially with the advanced controls VRC 470 VR10 stat and outdoor sensor
Going from an output of 17kw which I assume does the job ok for you to 28kw will give you cycling issues no matter what boiler you buy.

If you are sealing the system then go for a system boiler, a vaillant 618 would do nicely. You can still use an external vessel if you have larger pipes/radiators and need the extra expansion. They do a 418 as well if your keeping the system open vented. Underfloor heating will need to be mixed down in temperature so certainly doesn't need a more powerful boiler for that
I always wonder what installers are thinking of when they replace an 18 kW boiler with a 28 kW boiler!

Do they just not understand boiler sizing?

Or has the existing 18 kW boiler been unable to properly heat the house?


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