hope someone can help

[norfolkinesox]

i have a open vented heating system with a back boiler,the last two days the recirc pump has been noisy and a lot of air passing through defuser,the radiators struggle to get hot but once ive bled the highest radiator whole system calms down no air ,no noisey pump radiatiors become hot,everything normal
but when heating kicks back in later in day same again,system full of air

ive checked its not running over(think thats what you call it) no hot water going into expenasion were it can pick up air,even when i stop start it.
have you any ideas were to start?i cant find any leaks so air can get in(as yet)
i read about maybe desludging system and putting an inhibitor in -will this help

 

[seco services]

check the vent pipes not drawing in air .

 

[norfolkinesox]

thanks for reply,sorry to sound stupid,whats the best way to do that?also vent pipe does get hot so far up which is right isnt it?

 

[seco services]

put the vent pipe in a glass of water, does it draw the water up the vent ?

 

[namsag]

Tie the ball valve up and drain some water out the system and see if the water level falls in the header tank.
You could have a blocked cold feed

 

[norfolkinesox]

thanks guys thats giving me some things to try,really appreciate your replys

 

[gas4you]

Check you actually have water in the header tank

 

[norfolkinesox]

there is water in the header tank,another thing when trying to bleed radiators before heating kicks in ,there is the usaul hissing then stream of water,i can wind tap right out and a little hissing then stops and no water,im right in saying the water comes straight from header tank?but now when pump running its gurrgling through diffuser and eventually radiators are bled.
but then same again once turned off for a few hours
any ideas guys

 

[seco services]

sounds like you have a blockage in cold feed pipe.

 

[norfolkinesox]

after reading other posts it sounds about right do you have any tips to unblock it as i went up there this afternoon and pushed small rod up to first bend in pipe but obviously couldnt go any further.
is there some tool i could buy or use to force some pressure to maybe unblock it if its the probelm

 

[seco services]

you can drain the system then try a hose down the pipe in the tank.
or i've used a drain auger before but with the end cut off and freed the blockage before.
http://i.ehow.com/images/GlobalPhoto/Articles/2160260/drainauger_Full.jpg
or its a case of cutting the pipe out and renewing.


run a magnet down the pipe it will useally stick where the blockage is.
most common where the cold feed joins the system.

 

[norfolkinesox]

thanks mate appreciate reply ill give it a try tomorrow.