Vitodens 100W - hot water minimum flow

[masamune]

It may sound like a basic question, I have a newly fitted Vitodens 100-W, 35kW Combi.

When I turn the hot tap on the boiler is triggered a couple of seconds later and hot water is flowing. The pressure drops slightly, which I guess is the boiler compensating for heating the water timely in order to form a steady flow. So I have to open the tap a little more till I get stable flow of hot water at mains pressure. This is most likely a standard function of combi.

The problem is there is a minimum flow required for the boiler to "activate" hot water. And this is not a small flow, it's a lot of water which I find a waste when for example I need a small flow to wash tools or brush my teeth in the bathroom, or shave. If the flow is less the boiler will stop heating and cold water start coming out.

Is there any setting to the flow sensitivity for this function or is this hard coded into the boiler by the manufacturer? Just curious.

 

[Agile]

There are two aspects! The flow required to activate the boiler flow switch and the minimum power output of the boiler. These are both design functions of the appliance.

You have a very powerful boiler and if you must only take a low flow then you must understand that the minimum power output may be too high and cause the burner to go off an cycle causing the hot water to go hot/cold.

Everyone I know uses cold water for tooth brushing. To save water I don't use a running tap and just turn it on when I need the water for the toothbrush.

There is also another function that you don't seem to understand. Many taps are not flow stable when the water becomes hot and so reduce the flow rate as the tap heats up. That is the function of your tap and not the boiler!

Tony

 

[masamune]

Thank you, that makes sense.

Indeed you don't need the tap running for brushing teeth...but but...I don't like freezing water to numb my mouth

I hadn't realised the hot flow issue with the old tap. It wouldn't make sense if the boiler reduced mains flow lol. Its days are numbered!

 

[Agile]

It s not a feature of just old taps!

Most taps show this but to different degrees and you don't know until they are installed.

There is a brass jumper which carries the tap washer. This expands and becomes longer and closes the gap between washer and seating thus reducing the flow rate.

In theory they could make the jumper from an alloy with zero expansion coefficient but that would be very expensive.

Tony Glazier

 

[masamune]

It s not a feature of just old taps!

Most taps show this but to different degrees and you don't know until they are installed.

Tony Glazier

I certainly didn't know this, very insightful.

I suppose my Grohe in the bathroom was a good choice then

 

[Agile]

They are VERY good taps but then you pay for them.

I don't know how they compare with other models in this respect though.

Tony