Another pump sucking air down the expansion pipe thread....

[JamesB1976]

Ever since my CH system was installed over a decade ago the pump has seemingly pulled air back in through the vent pipe once the water got hot, if set anything higher than the lowest speed. I have had a plumber out once to revise the pipework (pump repositioned vertically rather than horizontal) but this didn't solve the issue. The layout looks okay (see photo below - cold feed on the far right, expansion on the far left and the vent pipe definitely extends more than 450mm above the F&E tank in the loft), but I have always wondered about the bores. I'm sure I've seen examples where the feed is 22mm and the vent 15mm, and this makes sense. However, both are 22mm in my setup - does this really matter?

 

[dilalio]

Seal it up mate!
My dad's place had a similar issue and that's what I did for him... rather than faffing about!
His CH has been perfect ever since - pristine system water and all rads piping hot!

 

[45yearsagasman]

Sealing it is one option, but this method is perfectly ok and is cheaper to do:-View media item 29821Before doing that, make sure all you pipe work around the H section is clean and you'll have no air sucked in.

 

[DaveHerns]

Just wondering but could you have some sort of one-way valve on the vent pipe?

 

[dilalio]

Just wondering but could you have some sort of one-way valve on the vent pipe?

No. The water level in it has to rise and fall with expansion and resistance.

 

[picasso]

Either the vent and feed are piped up the wrong way round or there is a severe restriction on the cold feed, if the pipes are correct I would look at the tee just above the pump, went to one a few years ago where the pipe going in to the centre of the went through and blocked the tee almost completely.

 

[45yearsagasman]

Do a simple test with a magnet all round the h section and the tees. Any attraction indicates a problem.