Central heating balancing on a two pump system

[craig1234]

Apologies if this comes across as a simple question but I would like some advice please on how to go about balancing my heating system which I have just enlarged to cater for a new extension that I am building.
The original heating system consisted of a Y plan setup with a single pump serving 9 radiators controlled by a single thermostat.
The new extension has three independent zones served by a new pump - there are a total of 11 new radiators in the extension.
The boiler thus has a single flow that splits to independently feed the two pumps.
So, my question is for balancing, do I treat the old and new circuits as separate entities i.e. ensure the new pump is not running and balance the old system (do I need to ensure the hot water is not calling for heat?) and then repeat the process for the new circuits ensuring that the old pump is not running or do I need to have both pumps running at the same time? Likewise, for the 3 new zones, in order to balance do I need to ensure that all valves are open or work on one zone at a time?
Thanks

 

[denso13]

Do the radiators all heat up or are you having problems?

 

[craig1234]

Denso, yes, all radiators heat up fine - just no balancing anywhere.

 

[denso13]

IMHO if you have 20 radiators and they are working ok i'd leave them alone.

 

[Hugh Jaleak]

+1.

Important rule of Physics. If it works. Don't fix it.....

 

[craig1234]

Hugh, Denso thanks for the advice.
Doesn't the system need to be balanced for efficiency though?

 

[craig1234]

All, despite my original thoughts, I now find that there is an issue with all radiators heating up when both pumps are running so I guess I will need to balance!
The problem is with 4 of the original gnd floor rads that are fed via drops from the 1st floor (the 1st floor rads heat up fine). If the extension pump is off then all original rads heat up so I presume that the new pump is taking too much of the flow.
So, I guess my original question still stands which is how do I go about balancing the system - have both pumps running and balance all at once or treat the two separately? I have reduced the speed of the new pump but that hasn't made any difference.

 

[Agile]

You should try to balance the rads using the lockshields.

The correct position for most lockshields is usually between only 1/4 and 1 1/2 turns open!

But it may also be necessary to balance the second pump using its OUTLET valve as well. Not strictly a correct method but often necessary to make it work reasonably OK.

Tony

 

[craig1234]

Thanks for the reply Tony - useful tip on the outlet valve adjustment.
But, should I balance the two "systems" independently or as a single entity?

 

[Agile]

Balance it with both valves open.

It will then work reasonably well with either one working.

Tony