Recent posts have described the d.2 parameter and the d.67 parameter, and the relationship they have to the period that the boiler waits before it tries to re-start.
One of the commenters (MikeH) reports having obtained good results with preventing microfiring by increasing d.2. Although my data suggested that this would not work in my case, I had not tried it. I now have, and indeed it does not help. Given my data, I'm not sure how it manages to make any difference for Mike.
Here are two graphs that show the period when I increased d.2. The first is just to show what was going in - the first two thirds or so, until about 5pm, shows a period of microfiring. There is then a transition to continuous burn when the target flow temperature goes up to 42C.
Now the same period, showing when d.2 was increased (from the default value of 20min to 60min) and what the countdown timer (d.67, in purple) was doing.
As expected, d.67 now starts at a much higher value - see the table in a previous post for how the actual starting value relates to the new maximum of 60min. But this has no discernible effect on microfiring, and certainly does not seem to have been the trigger for switching to continuous firing.
d.2 (via d.67) can be seen having its intended effect later in the day, at the end of the continuous burn. Then there is enough heat in the house, so the system needs to cool before the boiler can try again to maintain the desired flow. You can see in the following graph that d.67 does a full countdown from about 38min. This is what it should do, with these settings. But when the boiler tries to re-fire, it goes into an extended period of microfiring. This is what is should not do, and the high value of d.2 has not stopped it.
So how does d2 cure microfiring for me? The first point is that I may never have had microfiring as you know it!
ReplyDeleteIn the beginning I had all sorts of problems and repeated failed firings was in the mix. The worst of this was after Vaillant advised me to reduce d2 on a kind of simplistic logic - discontinuous heat = cut down the delays. This popped the idea of going the other way into my head and I have never looked back.
I thought it was going to be easy to answer this - just restate my previous pronouncements and job done. But! On a whim I decided I would just have a look at what my system does at 40C - territory it is never usually allowed to explore. What I expected to see was more of the same - after d67 expires boiler fails to restart, tries again "several" times and then gives up. Full recycling delay is then apparently re-established and may run to completion but would maybe start earlier by unknown agency.
What actually happens with flow target of 40C is subtly different. d67 expires and boiler fails to restart after a 15 sec burn. Then the state is s.7, the calling for heat icon is flashing and d67 shows 38 minutes. The 430 has however gone "off" although below room target temp. Time passes. After 16 minutes(+-) the 430 calls for heat again and now restart succeeds! This sequence repeats - full d2 followed by lesser period with 1 failed restart between each succesful. I'm now finding that the VRC430 is also going "off" during the full d67 count which is not what I expected.
This is actually pretty damned good and if I start to believe in it may lead me to reduce my VR430 minimum. It also leads me to propose a new mode of cycling - along with normal, short, micro and legionnaires we now have BICYCLING.
I wondered if "VRC430-anti-cycling-delay" might be anything to do with the pump delay parameter. Set that to off - no difference. Also set the mode from thermostat to none. No difference.
I have in the past seen behaviour in which the VRC430 takes over anti-cycling from the boiler. This has happened at higher temperatures when I'm trying to get a rapid room heat up. Sometimes it gets it wrong and then stops doing it and defers to the boiler. d2 isn't the whole story of anti-cycling. Boiler and Control are engaged in some sort of unholy alliance.
As a result of UpgradeMe's descriptions I have concluded that changes have been made to the boiler. I have written to Vaillant suggesting that they should Upgrade Me Too. I'm very concerned that I might get some improvements but also some additional intelligence which is fatal in the context of my system.
I think that your microfiring looks like it might be some new boiler or controller "intelligence" and it would be highly desirable for me if it could be better understood. I would very much like to hear a description of close observation of the boiler and control during microfiring.