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.
only reason i can think of constantly flowing water round the system is that it might balance the temp of all the rooms.
ReplyDeleteradiators will absorb heat if the water is colder than the room, can't imagine it being very efficient as leaving the internal doors open would have a similar effect
Congratulations on getting them to fix your system!
ReplyDeleteMy understanding has always been that problems may arise when the boiler, having cycled, tries to restart too early when the return water temperature + temp rise across boiler at startup exceeds target. With the original board, it isn't possible to avoid this
with flow temps below about 45C. Microfiring is some sort of super-bad behaviour when the boiler "thinks" it can try again very soon and is wrong.
Looking at your graphs, it seems that the boiler now doesn't try to restart until the system is cool enough (around 14C) for it to work. No failed restarts and no chance for microfiring to kick off? This was part of the changes I proposed they make - temp versus time to trigger restart. You can see 1hr 10 minutes actual delay. Doesn't happen on mine where max is about 40 mins and thus minimum temperature of 45C.
Running the pump all the time may be necessary when the boiler might have to restart so that the boiler can see the actual water temperature in the whole system rather than being confused by the temperature in the boiler itself. That may be cool enough
but hotter stuff come in when the pump starts. I have enough hot water in my well insulated main circuit for that to happen. Most systems, this wouldn't be a problem. You may be suffering from stuff put in there to benefit systems like mine.
Vaillant should try my intermittent pumping solution. Pumping in say 1.5 mins on, 3 mins off cycle is just as good and 1/3 the cost. Significant saving at 60Watts for the pump.
Looks like there is no change to the startup regime cos there is a 14c rise still.
I'm not sure whether I would be applying for this new board. Although it would "probably" be very useful I don't have a lot of confidence that unintended bad features might not be included. Better the (small) devil you know as they say. Maybe if I was going to move I would not be too happy about leaving new owners with trying to operate my system so would go for it then.