Rushing water sound when system is hot

[techno492]

Here's my problem

When my heating has been running for 50 mins or so I can here a noise of water rushing to the boiler and the Wilo pump is making a sort of gurgling noise.
This only happens after an hour of the system being run.

Any ideas ? Is it just air ? Do I need to do anything or will solve its self ?

If it makes any difference, I've just had the flow valve on the heating replaced as the old one wouldn't close when the boiler timer switched off. The plumber drained the upstairs only and I bled the upstairs rads 2 days ago.

Thanks for your help

 

[seco services]

Take it it's a vented system ?
Sounds like the systems not filling with water poss cold feed from f/e restricted/blocked.

 

[techno492]

Yep, open vented system

What could cause the feed from the f and e to be restricted ?
Any particular reason why I only get the noise when the system has been running for an hour or so ?

 

[seco services]

The cold feed can get sludge/crud built up from system corrosion over the yrs and go's hard and restricts/blocks the pipe.

check the f/e tank when it happens is it pumping over the vent pipe or is the water in f/e warm/hot ?
run a magnet over the cold feed area where it joins the system pipework, does it stick ?

 

[techno492]

Ill have a look in the f and e tomorrow. I've felt the expansion pipe and its only slightly warm as it goes up into the loft.

The house is only 2 years old, surely the feed can't get sludged up so quickly ?