Screeching pump and banging boiler

[RoyF]

The pump in our gas fired central heating system has recently started screeching intermittently, lasting for a minute or 2 when the boiler is running.
I've noticed that quite often when I turn the system off, the pump screeches for a few seconds as it stops. There is also sometimes a banging noise in the water pipe near the boiler just after the pump stops.
The pump was replaced almost 2 years ago.
There was a little air in the system. I've bled the radiators and boiler, and I'm waiting to see how it goes on. I also changed the pump speed from 2 to 3 (highest setting).
Any suggestions greatly appreciated.

 

[croydoncorgi]

Screeching from the pump is often a symptom of dry running (ie. no water in the water-lubricated bearing!!!). This is VERY BAD. The pump is probably badly damaged and needs to be replaced.
The banging from the pipes could also be due to insufficient water in the system.
Check your F&E tank (the little one) in the loft to ensure there's water. Open a bleed screw in an upstairs radiator with the system OFF and confirm that air (if any) then water comes out. If not, you have a blockage in the cold feed from F&E tank to rest of system.

 

[RoyF]

Thanks for the speedy response.

All the radiators get hot. No problem there. I understand your comments but don't see how the pump could have run dry.

I'll check the tank again. It was ok last time I replaced and bled a radiator. There doen't seem to be any blockage as system is working fine (apart from noises) as I've said.