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Sorry, I should have linked back to http://vaillantcyclingproblem.blogspot.co.uk/ more generally, since these questions are addressed in the preceding two posts there. This is still a prototype, and it does not yet have a code or name because it is not yet available, whether to buy or otherwise...

I am pleased to report that Vaillant has developed a replacement circuit board for the 400 series that seems to alleviate (or possibly obliterate) the problem of "microfiring" (i.e. rapid cycling), at least in my system. See my post at...

Actually, he recommended that we try it, and I still consider that to have been good advice. I already had the 4 series, before I'd ever even heard of weather compensation. It was therefore a choice of sticking with on/off controls for the life of the boiler (which was nearly brand new) or...

I am, I suspect, the 438 customer referred to in the post immediately above by ALEC1. I have been following this thread and others with interest since Alec added weather compensation (with VRC430f) in September to my existing 438, which was installed by others. Alec warned me before he started...