Open vent system water flow rate

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Current flow rate with an open vent system is 18 litres per min, as I'm converting to a combi system, what should I expect the flow rate be? the same, increase or decrease?
 
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Current flow rate with an open vent system is 18 litres per min, as I'm converting to a combi system, what should I expect the flow rate be? the same, increase or decrease?
How and where are you measurung the flow?
 
Hot or cold water ? Hot water flow rates from combi boilers vary depending on model / power but will be less than 18 litres per minute.
 
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The maximum flow rate of hot water will depend on the kW rating of the boiler and the necessary increase in temperature of the water passing through the boiler

Using figures quoted for the Vaillant 831.
Max output of 31KW gives deltaT of 35 degrees with a flow rate of 12.7 litres per minute

deltaT being the increase in temperature.

A 48kW boiler would provide 19 litres per minute.

Bear in mind that the boiler also has to be able to modulate ( reduce it's power ) to level that matches the heat required for heating the house.
 
This was measured at the cold tap

I assumed the question related to hot flow from the combi,

The cold flow at the kitchen tap would not be affected by fitting a combi provided no pressure reduction valve is fitted between incoming mains and the kitchen tap as part of the combi intallation.
 
At the kitchen tap
The tap could still be restricting the flow, depending on the type of tap. If you have a garden tap, measure the flow there as it will be unretricted. You should also compare the flow when the kitchen tap is full on at the same time.
 
Your cold tap if it is in the kitchen will be direct from the incoming mains supply not from an open vent tank
 
You do state the obvious don't you.

Perhaps not obvious to the OP... Or many others reading these threads.

I've lost count of the number of customers whom I've asked to show me their boiler, only to be taken to the hot water cylinder... We then have to traipse back downstairs.
 
The OP's first post was not clear, it did not specify which flow, hot or cold. So maybe stating the obvious was necessary
 
Apologies i wasn't clear, i wasn't aware that the taps run off the mains, out of interest the water tank in the loft what does this serve?
 
Perhaps not obvious to the OP... Or many others reading these threads.

I've lost count of the number of customers whom I've asked to show me their boiler, only to be taken to the hot water cylinder... We then have to traipse back downstairs.

Maybe the owner of the house wanted to get you upstairs D?

:ROFLMAO::ROFLMAO::ROFLMAO::ROFLMAO::ROFLMAO::ROFLMAO:

Andy
 

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