System Wont Vent

[ScottishGasMan]

Hi All, Having A little Problem Fixing A CH System.

Its an open System, 3 port valve, changed the 3 port yesterday as the body was passing on it, system filled up a treat, waters totaly clear.

when the pump runs its fine for a few seconds then you hear air in it, i changed the pump as it was an old weak thing to begin with, not has a grundfoss on it, tryed fitting the pump backwards to forece the air up and out still no luck.

open system on one level, header tank in loft looks like its a close coupled system, no blockages anywhere, pipes run from tank along 2-3 meters in loft then vertically down to pump pumping downwards to 3 port valve next to cylender (which has a working auto air vent)

any advice?

cheers
SGM

 

[gas4you]

header tank in loft looks like its a close coupled system,

Do you mean a combined fill and vent?

Is the vent or cold fill nearest the pump? If it is the vent it could be sucking in air.

 

[ScottishGasMan]

no its not compined, just close coupled (if thats even the right term) like the open vent + pump being within a certain distance, can even remember.

im sure the cold feed is closest to the pump, will have to go double check im parinoid now, am slightly suspicious that the horizontal run in the loft isnt venting back up the cold feed when the pump goes off, and maybe just lying in the pipes. Bloody Scottish gas fitters

 

[gas4you]

How about cutting an auto air vent in this horizontal pipe run?

 

[ScottishGasMan]

hey, cheers for the reply, double checked and the cold feed is def closer to the pump than the vent,

might need to cut an auto/manual air vent in there. If i stuck an auto air vent in that would be half way between the cold feed + Pump, would the pump not suck air through the auto air vent?

 

[gas4you]

Stick to a manual vent then