Combi boiler pumps

[mth]

Hi

My combi has two pumps in. In the manual, it says one is DHW and one is for heating.

They are both Grundfos 20/60 with adjustable speed settings of 1-3.

By default they were both set to 3. I changed the central heating one down to 1 as it sounded like a jet engine inside the house with the water rushing around my pipes!

What does the DHW pump actually do? What affect will changing the speed on this have? The speed at which the water comes out the hot tap is determined by the pressure of mains - correct? So does this pump move the water through the heat exchanger at different speeds?

Thanks.

 

[Agile]

Sounds like something out of Greek mithology!

The DHW pump should be on max to put the heat into the DHW.

Ther CH one would usually be on 2 but if 1 still gives enough heat then thats OK. The temperature differential between flow and return should only be about 11°C and it could damage the boiler if this were greatly exceeded on setting 1.

Tony

 

[mth]

Thanks Tony.

I'm still not quite sure what this DHW is actually pumping It doesn't seem to make any difference to my DHW when I turn the pump down from 3 to 1. It still flows out fast and it's still very hot.

...but if 1 still gives enough heat then thats OK.

I'm assuming it's OK, all my rads are too hot to touch when the systems on and has warmed up nicely

FYI I have a new Firebird condensing boiler 20kw