ch system noisy when on hot water

[reevesie]

potterton kingfisher, 3 port valve just had new pump fitted (set on 2). (3 bed semi)

when ch and hot is on or just ch, all is fine no noise.

When hot water only makes lots of racket as if lots of air is in system.

Bled the radiators, valve and pump.

any ideas? the plumber said there may be some noise but that should go after bleeding the system a couple of times.

also the old pump was set on three the plumber said 2 is fine? Is that right?

Just want to get some idea b4 calling the plumber back

 

[ChrisR]

Check the small tank in the loft to see if it's "pumping over" ie water coming out of the vent pipe above the tank. If so the system design is wrong. Try it on speed 1 just to see if it stops. ANd try speed 3!

Speed 2 is probably ok - see if the boiler cyles on and off while the rads are heating up. If so try speed 3