hot 22mm pipe

[Dannyparty92]

Had our opened vented hot water cylinder swapped for a combi boiler. The DHW pipe from the boiler is in 22mm all the way to its final draw off which is the bath. since the swap the flow at the bath hot water tap is poor. I thought it would be much better flow as the hot is now running off the mains. Thanks in advance for any anwsers.

 

[payney1974]

Depends if your mains are any good mate.

 

[payney1974]

Don't forget a combi has to heat the water as it passes through the heat exchanger, if it flows through too fast the water won't have enough time in the heat exchanger to capture enough heat.


With your old cylinder you had a mass of hot water that can flow as fast as the tap will let it.

 

[kirkgas]

The original flow was gravity and the pressure would be 0.1 bar per metre height from the water level in the loft tank down to the tap, at a temp of 60 degrees, the flow is now mains and determined by what is coming in, added to that is the flow restriction required to maintain a decent temp rise, some combis deliver 10-13 litres/min at a temp rise of 35 degrees so its easy to see where people aren't happy with the result, a point which should be fully discussed by the installer before the job is done

 

[StillLearnin]

Check the specified flow rate of the combi (in it's manual) and then check at the tap that it is somewhere around this

 

[Dannyparty92]

so its pretty much the heat ex in the combi and the oversized 22mm pipe thats causing the flow to be poor?

 

[Mike Jackson]

What size combi is it?

 

[Dannyparty92]

24kw mike.

 

[buckley plumb]

24kw mike.

most 24kw boilers are restricted to 8 litres to allow 40 degrees temp rise

 

[Dan Masey]

What do people mean by a temp rise? As in the temp of the cold mains to the temp at the hot tap?