Two pumps on heating system. Imbalance?

[Vavavoom]

Hello, I wonder is I could ask for some advice please.
I have just replaced and only gravity fed boiler with a new Baxi heat only boiler.
The system is two pipe and has 17 rads in a long old house. The system is 22mm copper except the last 5 rads which are 15mm. (I know this should be no more than 3 but changing isn‘t easy)
The system has 2 circulating pumps, and is now a Y plan system.
one pump is in the airing cupboard close to the HWC and the second close at the end of the 22mm but before the last 5 rads.
The pump in the airing cupboard has been changed to a Grundfos UPS3 and the second remains the same.
Both come on and off at the same time.
I now have a problem where the far part of the system heats up quickly and the nearest part to the new pump is very slow. I have balanced the system and the far 5 rads are almost closed on the lockshields. Only when their TRVs close do the other rads heat up well.
my question is should I switch off the second pump / or remove completely.
My concern is the second pump is pulling all of the flow from the first part of the system, does this sound about right?

 

[ShaunCorbs]

Is it open vent or sealed ?

 

[Vavavoom]

Is it open vent or sealed ?

It is open vented.

 

[ShaunCorbs]

Ideally you want to use a 25-80 pump but chances are your going to pump over back into the tank so might need to seal the system

 

[Vavavoom]

Ideally you want to use a 25-80 pump but chances are your going to pump over back into the tank so might need to seal the system

Thanks, so would the 25-80 replace the pump by the HWC? and if so remove the second pump or would the water flow through it if just disconnected electrically?

 

[ShaunCorbs]

Yes and no need to remove it completely

 

[Vavavoom]

Yes and no need to remove it completely

Thanks for the advice, I wasn’t sure if the water would still flow the stationary second pump.