Vent Pipe of F & E Tank Sucking Air

[Harvo]

Hi. This relates to a post I put up on 19/11/08, but there’s now been some progress. The problem relates to air continually getting into radiators and the F & E tank filling with hot water and overflowing when the central heating pump is running. The system is about 40 years old, open vented, gravity HW and pumped central heating.

Last night I put the end of the vent pipe over the F & E tank into a jug of water. This morning it was empty (600ml gone) proving that the vent is sucking and probably explaining why air is entering the system. The F & E tank is also full of some fairly murky, dark red/brown water.

Question now is, why is it sucking and what do I do about it?

 

[andrew5235]

I had a similar issue and turned the pump down to position 1, radiators still getting as hot, if not hotter as ther is no air getting into system. Worth a try.

My system is also old, about 30 years and was always getting air into it.

Thanks
Andrew

 

[JohnD]

as you have rust and sediment, you need to fix it soon or your rusty radiators will leak. Unless the system has been doing this since it was new, due to a design or construction fault, you probably have a gradually-occurring fault such as sediment causing a partial blockage and interfering with the proper flow. This is very common with old open vented systems.

Start with a chemical cleaner like Sentinel X400, which is very mild and you can leave it circulating for 4 weeks before draining. If the water goes inky black soon after you add it, that shows it is breaking up existing sediment. Bale and sponge out any mud from the F&E tank first.

If you hold a strong magnet to the copper pipes, especially where the ones from the loft join onto the bigger circulating pipes, probably near the pump, they will be attracted to any collected black sediment (which is a magnetic form of iron oxide).

If you are fond of DIY plumbing, and have a sediment problem, and can afford £100, it is worth fitting a Magnaclean on a vertical 22mm Return pipe, and it will trap any circulating black sedinent that has been loosened by the chemical, and will prevent future black sediment being able to collect into new blockages.

 

[Deleted 98600]

are you able to determine which side of the cold feed and vent the pump is and if the system is un der negative or positive pressure?

http://www.pumptool.co.uk/Position.html

have a looknat this link and see if you can determine which system closely meets yours. there is a neutral point at which thw cold feed and vent should be connected