I have found that its software has also been improved in another respect. I noted in the post here that the anti-Legionella programme (which was supposed to heat the hot water cylinder to 70C) did not work correctly, with heavy microfiring apparent. This has changed, with the behaviour now looking like this:
It's not perhaps perfect, but it's certainly a vast improvement. Now the target flow temperature used is 70C (rather than about 84C), and more importantly there is no microfiring because the boiler stops trying to heat the cylinder when it reaches a temperature above about 65C. So I shall be content to use this programme, whereas I certainly wasn't before.
It is not that the anti legionaire has been modified it is because the boiler now does not overshoot after the inevitable cycle that happens when heating dhw. Before you got the board the boiler would set a high target flow and water storage target, the return temp would gradually get to within 5c of flow and the boiler would cycle, however you would have a lot of latent heat in the cylinder that would be surrounding the flow and return much like insulating the pipes in a medium at around 65c the boiler would re-fire at 80% of max rating regardless of what you set the rating for DHW generation and cycle like crazy. This is exactly what I have been demonstrating to Vaillant all this time.
ReplyDeleteUnhappy Vaillant,
DeleteI believe the anti-legionnaire programme has in fact been changed (although I entirely agree that part of the improvement is also due to the fact that the boiler does not now enter the quick fire-stop-fire-stop cycle).
To see this, compare this graph to the one in the earlier post to which I link above, which has a similar graph from the old board. The target flow with the old board was 85C; the target flow now is 70C. This is not something that I have changed (or could change), so I conclude that it is a change made to the legionnaire programme. Furthermore, the old board did not apparently stop trying to heat the water until it had reached a temperature of 85C; the new board stops trying to heat the water even though it is still only in the high 60s (although admittedly it could have stopped earlier than it does).
Even the new programme is not right to give the advertised behaviour. The legionnaire programme is supposed to heat the water to 70C. This is never (or at least not without a good degree of cycling) going to be achieved with a flow temperature of 70C. What it ought to do is use e.g. 75C, and stop when the water reaches 70C, which it should be able to do without any cycling - see the graph above, where the tank temperature gets up to within 3 or 4 degrees of the flow temperature before the flame goes off.
But I am content that my cylinder is in the high 60s for at least a couple of hours, since that will kill the bacteria.
I see I agree 100% that changes have took place, shame it isn't quite right still on what it should be doing. As you say mostly it is the start up behaviour that now allows subsequent burns actually to get some heat into it.
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