Vallant Combination Unwanted Hot Water Taps Flow Adjust...

[TonyHa]

I have a Vallant Ecotec basic combination boiler installed at my house in Scotland in late 2009.
It has this annoying feature of turning the hot water taps output down and up a bit without my permission (all or most in the house);
(My friend where I stay a lot in London has an older (and much bigger) Vallant Ecomax boiler I had installed for him in 2005 and it doesn't ever do this).
For example:
1) I know there is residual heat in my boiler hot water plate heat exchanger and I want to wash my hands in the kitchen sink (right by the boiler) without triggering boiler to come on again). If I turn on tap just a trickle the boiler quickly strangles the flow to off. (My friend's boiler does not do this). So I turn the tap on just a little more and I can use the residual hot water OK, until its goes cold which I like.
2) When it goes cold my boiler very shortly automatically turns up the hot water flow a bit (without me touching the tap) so the boiler gets triggered again. This means that I have to quickly turn the tap off as soon as the hot water gets near cold to stop the boiler coming on again and wasting gas.
I don't want any of this automatic adjustment and my friends boiler doesn't do it.
I have checked the engineer's settings (including the concealed ones) and I cannot find one to get rid of this feature though I admit I don't understand the descriptions of them all and would appreciate it if you can let me know one I might have missed or a part I can get changed inside the boiler to get rid of this feature. I am an electrical engineer. Thanks!

 

[Jurassicspark]

Hmm, that's part of the normal operation. When you open the tap slightly, there is still hot water left in the pipes and the boilers flow switch doesn't detect a demand for HW, therefore it shuts down. When the water runs out the boiler draws more from mains and the flow switch turns back on.

If the boiler already heats the water to say for example 50C and it turns off, then turns back on, not much gas is consumed compared to starting from a lower temperature in the morning.

(My friend where I stay a lot in London has an older (and much bigger) Vallant Ecomax boiler I had installed for him in 2005 and it doesn't ever do this).

That depends on the pipe distance and what tap is in use.

 

[TonyHa]

How come the Ecomax boiler of my friend's doesn't do it then, (as I said)- why should a boiler modify the WATER flow rate. It should only react to the flow rate the USER has selected at the water tap outlet- if not enough to trigger the ignition sequence to leave it running at the very low flow rate cold. If the user turns the water tap on a bit more THEN to trigger the ignition sequence when the rate is enough otherwise not. AsI said this is the way my friends Ecomax 2005 boiler works and always has. It may be that since that 2005 boiler Vallant's newer ones in a well intentioned effort to maintain water heating even at very low flow rates automatically interferes with (increases) the user's selected water flow rate from their tap to start the heating but I say a boiler should ONLY react to what the USER has selected and not have a ("smart"?) mind of its own and interfere with the user's selected hot water tap flow rate. My friend's boiler has always worked that way and he and I have been and remain very happy with it. Perhaps you hadn't noticed that Vallant (and other manufacturers?) had made this change? But thanks anyway for making the effort to reply.

 

[CountryFan]

Are both boilers you’re talking about combi boilers? Perhaps the Ecomax has a different flow rate to trigger the boiler.