Selecting the correct pump size for a central heating system

[nairb999]

I replaced a Myson CP 63 for a Circulating Pump CP63. Are they like for like? - Circulating Pumps were not able to help me.

The reason for the question is looking even further into the continuing saga of air in my system.

After asking many questions on this forum I have changed the pipework twice and chemically cleaned twice so before I try anything else I want to be a little more confidant in the outcome.

I believe I now have the pipework correctly set out plus the system is clean and inhibited.

So as my problems became worse after changing the pump I am now wanting to know is the pump the right size. Circulating Pumps have suggested I fit the 53 but I feel this is a bit hit or miss.

The boiler is a Potterton Prima 60F supplying 16 small radiators. How do I work out the correct pump required ?

 

[ChrisR]

The company Circulating Pumps used to be the maufacturer of Myson pumps.
Give or take some minor update, it's the same pump.
Pump size depends on system resistance, which you can't really measure. A CP63 is not a lot more powerful than a 53, and you can always turn it down - in fact you should do a balancing exercise which would tell you if the pump is ok or not. The idea being that the pump should be able to get the heat out of the boiler to the rads, so the boiler shouldn't cut out when on max, until the rads are all 80 or so on the flow and 70 on the return.
If there's a fixed bypass it will screw that up, though, because the boiler will heat up faster than the rads.

 

[nairb999]

Many thanks Chris R

A CP63 is not a lot more powerful than a 53, and you can always turn it down - in fact you should do a balancing exercise which would tell you if the pump is ok or not. The idea being that the pump should be able to get the heat out of the boiler to the rads, so the boiler shouldn't cut out when on max, until the rads are all 80 or so on the flow and 70 on the return.
If there's a fixed bypass it will screw that up, though, because the boiler will heat up faster than the rads.

Yes I do I have a fixed bypass ie radiator in bathroom with 2 lockshields.
On setting 1 all radiators heat up very quickly. Although my system supports 16 radiators only 3 are double and not particularly large and the rest are singles ranging from tiny to small. So my thinking was with the equivalence of fewer radiators say 8 the pump even on its lowest setting is creating too much suction on the primary side

 

[mickyg]

have you combined the feed and vent?

 

[nairb999]

have you combined the feed and vent?

Mickyg - I do thankyou for your suggestion and I probably will I am just exploring all options