Vaillant ectotec Cycling Problem

I see oversized boilers on a daily basis. Perfect example today was a Vaillant 637 (37kw) when a 624 would have done it perfectly well (12 rads). The difference is that the 4 series fires on high rate where the 6 series starts on low. If you oversize a 4 series it will cause more issues than the 6 for that reason. Size it correctly and the 4 series in theory will heat up faster than the 6 though, that's the advantage. The new 4 series is totally different and they've had to make it start on low to account for idiot installers who don't know how to size a boiler correctly.

I have been banging on about this for years. I got sorted with a dev PCB, havent seen a new one in action but glad they eventually sorted. The rumour was that it started high due to NoX emissions compliance more like stupid logic. It was so difficult to get it to hold a burn when a low flow temp was requested. Bit of messing with anti cycle timer could sometimes get you in the ballpark. I have a couple of really old installs with kingfisher2's and Stelrad 60, with this knowledge I would consider the 4 series for sure. Here is a graph of my 428 behaving itself nicely. This is two calls for CH and 3 DHW partial draw off's

fook me i bet your tenants love you

They do Nightmare tenants slum landlord it aint. But seriously currently currently in dialogue with inspire home automation to get an automated alert (push or email) if boiler calls for heat and no heat rise, have fixed 2 issues (two different properties) before tenants knew there was an issue. Both occasions where someone meddling when clock change has took place (must have seen Mum or Dad running round the house changing timers).