Rad needs bleeding twice a day

[zigg]

The radiator in our bathroom (12x18) fills with air at least twice a day! It has always needed bleeding every few days or so, but has suddenly gone silly. As I bleed it, I can hear air bubbling into it, and if I wait after bleeding, there is a semi-constant "bloop......bloop-bloop......bloop" as air is finding its way into it. The pump has always been noisy ........when it starts up there's a whooshing sound, obviously lots of air being pulled through.My first thoughts are that it's being sucked down the expansion pipe......but why has it suddenly gone crazy?
The water is clear too.........pump on speed 2 (regular Grunfoss pump)
Any thoughts? (sitting here, scratching head)

 

[JohnD]

Have a look in the Feed and Expansion tank and see if

1) it has water in it
2) it is pumping over from the vent pipe
3) it is full of mud

When did you last put inhibitor in it?

 

[LUNAT]

HI


Old systems were sometimes designed wrong.eg incorrect positions
of feed and expansion pipes which either causes water to pump over or air being sucked in.if this is the case then it will need altering.

 

[zigg]

Thanks guys. JohnD, I last put inhibitor in last summer, after backflushing all rads, in both directions. I'll have to wait for the weekend before I can check things up in the loft tho, will get back to you on that.

 

[AshaDPlumber]

I have come accross this a few times, more so recently for some reason. I've been finding it's negative pressure caused by your cold fill being on the return as apposed to the flow. Why this would have gone crazy recntly is beyond me, but the best way to find out is to either,

1. put a check valve on the vent pipe to stop air being sucked back in, but ymake sure you take it back off straight away cause it is dangerous to obstruct the vent.

2. Look in the F&E tank to see if it swirls. Generally it will if you have negative pressure.

Hope this helps, obviously it won't fix the problem but will explain what is happening