First day of full data collected from new circuit board

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.

Promising signs

On a couple of mornings so far, since fitting of the prototype board, there has been a call for heat. Unfortunately vrDialog does not recognise the new board, so will only collect a small subset of the data that it used to collect. This makes it much harder to monitor the behaviour of the boiler, but yesterday I made manual observations during the 40 minutes or so when there was a call for heat. The signs are good:

There was a continuous burn throughout this period. Thus the boiler was able to sustain a flow temperature at the boiler of 35C or 36C, which I've never seen it do before - typically before it would microfire below about 42C. One slight oddity, though, is that the flow target temperature throughout this period was 28.5C, which doesn't bear any relation the the actual flow temperature (whether at the boiler or at the low loss header, from where a probe is now also wired in to the boiler).

Pending further data, the new board therefore looks as though it may be an improvement over the standard one. All is not quite right, though, since the central heating pump now sometimes stays on all day, even if there has been no heating demand at all, circulating unheated water through the radiators.

Prototype circuit board

Having given Vaillant over six months, in which time - as expected - I heard absolutely nothing from them, last week I sent a letter before action, with the intention of issuing a claim if matters were not speedily resolved.

As if by magic, yesterday I received a call from Vaillant's Product Manager (whom I emailed in November, December and January without ever receiving a response). Today he and the Senior Engineer visited and fitted a new circuit board to my boiler (and gave a welcome apology for Vaillant's failures of communication). He also today fitted such a board to one other person who has been suffering the same sort of problem.

It is a prototype that has been developed in France with the intention of ameliorating the difficulties that I have described on this blog. It has apparently so far only undergone testing within Vaillant, and they now want to try it on the two 'real life' systems on which they fitted it today to see how it performs. I was told that if it is successful, it will become a standard part available for purchase. I have no information about when (or indeed if) that may come to pass, not least because it will take a little while to assess how well it works. For the time being, it is not otherwise being made available.

As to what has changed, the information was a bit vague, which is not a criticism since it may be hard to describe at a high level. I gathered, though, that the focus has been on the ignition sequence and timing.

As the weather cools down over the coming month and the heating starts to kick in, it should become clear whether microfiring is still an issue.