The new circuit board is progressing well. I have now found a way to persuade vrDialog to collect comprehensive data from it, which reveals no microfiring on the first day I did so, despite a flow temperature in the thirties or low forties:
This is a very considerable advance over how it would have behaved with the old circuit board, which I'm sure would have given microfiring throughout a day such as this. However, I've noticed that there is a bit of a tendency for the house to overheat. The heating curve is already down at a lowly 1.3, and room temperature control is set to "modulating" (which is where I'd like to keep it if I can, rather than going to "thermostat", but I may have to stick to "thermostat" until winter is upon us).
Those with a sharp eye will note that this graph looks a bit different from ones that I have posted previously. That's because I now have an external temperature probe at the top of the low loss header (where the 'flow' pipe leaves), which gives a more realistic measure of the flow temperature than the temperature of the water leaving the boiler. The two can differ because of mixing in the low loss header. The boiler now modulates so as to achieve the desired flow temperature in the low loss header.
Previously, the "Flowsetpoint_DK" (i.e. the target flow temperature) tracked very closely the "BMU_FlowTempOrVF_1.Temperature" (which is the flow temperature as measured in the boiler). Now, however, Flowsetpoint_DK is the target not in the boiler but in the low loss header (LLH). You can see for instance in the long, continuous burn at the start of the day (when Statenumber is 4) that a flow of 36C or 35C is being successfully maintained in the LLH. Presumably the return temperature is gradually increasing over this period, so mixing results in less of a temperature drop of the flow in the LLH, with the observed result that the boiler flow temperature (blue) required to maintain the desired LLH flow temperature (red) gradually decreases until the two coincide, which is roughly the point at which the flame switches off.
I should note for completeness that the LLH temperature probe has nothing to do with the disappearance of microfiring; it was fitted in April, and I was still seeing microfiring when it was there. It is definitely the new circuit board that has alleviated - or hopefully removed - the problem of microfiring.
As to the strange pump-on-all-day behaviour that I mentioned in my last post, I am told that this is a normal and deliberate feature under some circumstances, rather than a problem peculiar to the new circuit board. I can't see the point of it, though, so I'd be glad if someone could point me to a parameter that will stop unheated water from being needlessly pumped around the radiators (beyond the pump overrun time) - I can't see one on either the boiler or the VRC430f that sounds as though it might control this.