Pump has been a bit weak ever since we bought the house. Now getting
noisier and less effective.

Ideas for a replacement please.

House is 3 bed detached reasonably well insulated in Essex. 2 storeys
about 500 sq ft each.

All pumped system. Boiler is a 24HXI, usual 25mm pipes to ordinary rads.

We get some horrible airlocks so something that is easily bled and with
a bit of oomph would be good.

As usual it is in a position where it would be difficult to change the
pipework. Prefer one that would fit the same as the Myson.

TIA for any advice.