The VRC430f includes an anti-Legionella programme. Legionella can lead to the fatal Legionnaire's disease, and is a problem that can arise when water is kept within the bacteria's growth range of about 20-50C. I set my hot water temperature to 48C, since that's as hot as it needs to be for our hot water needs. But that means that the system is at risk of a Legionella infection, so I decided to try a once-weekly anti-Legionella programme.
It's supposed to heat the cylinder to 70C for one hour to kill the bacteria. However, it doesn't work as advertised. It uses a flow temperature of 85C and just tries to keep going at that temperature, despite the cylinder temperature (green) exceeding 70C:
As soon as the cylinder temperature is above about 70C, the difference between flow and return is not high enough for continuous firing. The result is that the boiler cycles rapidly for about two hours, with the cylinder temperature gradually rising to 85C. The jagged lines in flow temperature (red) and state number (light blue) represent cycling. Just as with microfiring, the boiler does not stay ignited for more than a few seconds before it turns off again, and then it tries again shortly afterwards. I'm not convinced that it's doing my pumps a whole lot of good to be too hot to touch, and it's definitely not a good thing for fuel efficiency or boiler longevity to be short cycling like this.
This is all with the boiler's flow temperature for cylinder charging (parameter d.78) set at 70C (orange), so the VRC430f must be over-riding that. The central heating demand in the graph starts at 6am (as you can see from the HC1_QuickVetoTemp), and is not affecting matters.
So not even the Legionella programme works correctly. Another software problem with the VRC430f, it seems.
Not a problem with the VRC 470 it is the boilers logic once it cycles. The same would happen on basic controls.
ReplyDeleteActually, it is not the cycling that is the extra problem here, since it is (presumably) just another manifestation of exactly the same microfiring issue that is seen during central heating operation.
DeleteMy point was that there is an additional problem specifically with the Legionella programme, which is that the system continues to try to heat the water even when it is above 70C. It ought to stop when it reaches 70C (and if it did that, it just so happens that it would hardly if at all reach the stage of cycling).
However, I believe that (even though the Legionella programme is provided by the VRC430f) you are quite right that this additional problem is not one in the VRC430f software, since a more sensible flow temperature of 70C is used by the new boiler circuit board - see post of 2 October, on which you have also commented.