Well if we go with your flow of 0.2 kg/s for 5 secs, that's a litre per activation. Over 20K activations that's 20 cu m of water at say £3.20 per cube including disposal. So you get another £60 out of it that way.
On a combi fired from cold it will probably run full on until the primary HE and primary water are up to temperature. Only when the temperature on the return from the PHE starts to rise will it modulate (if its one that can)
OK - (I'm not on a water meter, didn't have the costs to hand).
In reality I expect the valve might have died after 20,000 activations.
And how many years is that I wonder...
Lets say 5 activations a day, where the boiler is cold - seems reasonable.
4000 days = just under 11 years. I bet the device would be buggered by then :)
You lose a bit less, as the water isn't running full while the heat exchanger heats up. It's not about the water in the leg, it's about the water in the heat exchanger. Though you also lose less in the leg, as the hot water going through it is hotter.
That assumes the boiler will run up to full output on a reduced flow.
I thought that they all did that and that it was part of the current standard
tim
This is what I was thinking, but getting the wife/kids to do it.....
Yes, I understand ...
Mine does (15yo Vaillant) and it is switchable.
There are lots installed ones that don't - it may well be more common on new models now - can't say I have done any exhaustive checking.
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