Central heating sucking air through vent pipe

[Jock Spanners]

Evening all,
I've just changed a Keston system boiler for a regular Worcestor with a pump. The customer had bought the boiler mistakenly thinking it was a like for like swap. I've added the pump and everything seemed fine but a week later he's complaining about air in the system and the F&E tank overflowing. I'd replaced the float valve and probably didn't bend the arm enough as there wasn't a lot of room for a 18 rad system. I've adjusted the arm further. I suspect the air is being sucked in through the vent. It's an S plan in a three storey house with the boiler and cylinder in a cupboard on the middle floor. The pump is on the flow pipe. The rads are all knackered and he didn't want a powerflush as he didn't think they would stand it. I agreed and tried to flush as much of the sludge out with detergent. I've turned the pump down. Has anyone any ideas what I can do? From distant memory I seem to think a 'wet vent' might be the answer but I can't remember how to do one. Any advice appreciated.

Jock.

 

[Harvest Fields]

Is the F&E tank raised or on the floor in the loft? Are the feed and vent pipes combined?

 

[Jock Spanners]

Is the F&E tank raised or on the floor in the loft? Are the feed and vent pipes combined?

The F&E tank is on a platform in the loft conversion. The feed is to the return. The vent is separate.

 

[Harvest Fields]

The F&E tank is on a platform in the loft conversion. The feed is to the return. The vent is separate.

Try combining them unless anyone else has something else to say.

 

[townfanjon]

You will have to close couple the feed / vent etc .
First pipe off the flow pipe , next vent , next pump . All within 150 mm .

 

[Jock Spanners]

You will have to close couple the feed / vent etc .
First pipe off the flow pipe , next vent , next pump . All within 150 mm .

Currently on the flow there's a 15mm stem pipe to an auto air vent above the boiler teed in before the pump. Are you suggesting teeing in the feed, then the vent before the pump and should I dispense with the stem pipe?

 

[townfanjon]

Currently on the flow there's a 15mm stem pipe to an auto air vent above the boiler teed in before the pump. Are you suggesting teeing in the feed, then the vent before the pump and should I dispense with the stem pipe?

I would yes , the close coupling system works . As said , feed first , immediately after vent , then pump , all on flow pipe , that wont suck any air in as its all under positive pressure . Ok a bit of work involved I will admit .

 

[Jock Spanners]

Like this?

 

[townfanjon]

Like this?

 

[townfanjon]

Yep , bo**ocks I said feed first , appologies its been a long day .