Air sucked in system

[bobby_la_mesma]

Hi

I've tested my system and found that air is being sucked down from the expanion tank, overflow pipe. I want the system right so should I re-arrange the piping or just fit an aerjec de-aerator?

My system F&E tank is only about 50cm above the top of the boiler as I live in a bungalow. Is this the cause?

Thanks

Rob

 

[ChrisR]

New, old, boiler model, existing arrangement of pump, etc etc ?????

 

[Agile]

Its always better to have at least 1 m above the boiler.

This sounds like a prime candidate for a combined feed and expansion pipe.

Raising the F&E tank should also be done if its at all possible.

Tony

 

[bobby_la_mesma]

How do I combined the feed and expansion pipe? I have a Worcester Greenstar 30CDi Conventional in S layout.

http://www.worcester-bosch.co.uk/index.php?fuseaction=product.detail&con_id=127781&detail_id=129082

The link above is the layout I copied when installing the boiler. It shows a seperate F & E pipe. Is it still o.k. to combine it?

My layout has a 22mm vent pipe on the flow side of the boiler, before the pump. It T's into the system from above the Flow pipe. A 15mm cold feed pipe the T's into the system immediately after the vent pipe. The cold feed pipe T's into the system from below the flow pipe. The pipe then travels down the wall to the pump. The pump, pumps downwards towards two valves. One valve for the CHS and the other for the HW tank.

 

[bobby_la_mesma]

This is a photo of the layout. On the left is the boiler. This is all in a small cupboad so fitting an aerjec is going to be really difficult.

http://www.flickr.com/photos/11764523@N05/?saved=1

 

[bobby_la_mesma]

Sorry,

My manners temporarily disappeared. Thanks you both for your tips

 

[Agile]

Take the 15 mm feed off the horizontal 22 mm pipe and cap the cut pipe.

Fit a "T" about 100 mm or more up the vent pipe above the horizontal pipe and connect the feed to it.

Some people take the feed down 50-100 mm or so before taking it up to the connection point in the belief it reduced thermal currents. Not really necessary though.

This is not recommended by everyone but I have used it on numerous occasions to solve problems like yours. It has always worked for me!

Tony

 

[bobby_la_mesma]

Thanks Tony

That solution sounds great. I'll re-arrange the set-up ASAP

 

[chrishutt]

As a matter of interest it shouldn't be possible to suck air in via the 22mm vent (not "expansion") pipe since the connection of the 15mm feed and expansion pipe represents the neutral point of the pumped circuit. Pressures lower than static (0.5 metre) should only exist upstream of the pump up to neutral point (e.g. upstream pump isolating valve gland nut).

The vent pipe connection would normally have a marginally higher pressure than static. If air is being sucked in via the vent it suggests that the F&E pipe is blocked, probably near it's connection with the flow pipe. However the whole installation pipework looks quite new so unless it's a modification of an old system you wouldn't expect to find a blockage.

 

[gas4you]

Is the 22mm pipe that t's in to the pipe work above the pump the cold feed?

If it isn't then the cold feed is in the wrong place and I can see why it is sucking in down the vent.

 

[bobby_la_mesma]

Hi All

The vent is the 22mm pipe that T's into the top of the horizontal pipe, above the pump and on the left hand side of the picture.

The cold feed is the 15mm pipe that T's into the bottom of horizontal pipe, after the vent and before the pump.

Thanks

Rob

 

[gas4you]

Oh yeah. The shadow made it look like 22mm to me I would be tempted to turn off cold fill gate valve and crack the t to see if it is blocked.

I take it you have checked there is water in the f&e tank?

 

[bobby_la_mesma]

Hi

Checked the cold fill pipe and it was free from any blockages. The F&E tank is also full.

Cheers

Rob

 

[Dan Robinson]

That must have cost a fortune in compression fittings

 

[giblets]

As a matter of interest I am having a similar problem with a system at the moment (sorry to hijack yr thread, Bobby )

28 flow rises vertically off the boiler into a 28x22x28 tee. (22 vent rises some 3m to the feed tank.) 28F runs horizontally from this tee. 125mm along the 28F the CF is tee'd into the underside in with a 28x28x15. 28F then goes on to pump. S-plan layout.

When the rad circuit comes on the level in the feed tank drops by about 10mm. When the rad circuit is turned off (and pump stops) the level in the feed tank returns to normal but a quantity of water is expelled from the vent pipe into the feed tank. A container of water held over the open end of the vent pipe indicates air being expelled from same on start-up. No over-pumping whilst operating. This only happens when the rad circuit comes on. No probs with the HW circuit.

Any ideas, folks?

BTW feed pipe is not blocked.