Hot water keeps drawing in air, pipework incorrect?

[Plumb Tidy]

Hi lads and lasses, I have this customer that has to keep forcing mains pressure back through his vented hot water system every week due to a blockage or air as he explained it. He said it has been like it since he has moved in but has got progressively work he has been there for around 6 years i don't know how he has put up with it. Its a 3 storey house two bath rooms, both showers run off a shower pump.

I took a look today as i have done some work on his central heating system the two things i have found to be a bit odd is that,

1.The hot water draw from the top of the cylinder exits the cylinder at a downward angle(excuse the photo the angle looks fine but in real life its going down). To my knowledge this should be going at a slight upward angle to stop the air locks occurring as air can travel towards the rising vent.

2.The Vent pipe is directly above the cylinder outlet i believe this should be at the end a the 450mm rising outlet run.

3.The shower pump that feeds two showers is drawn off by the tee on the 450mm downward pipe which is ok but not great as this could contribute to air problems as there are better connections to be had.

If there are any thoughts or advice to my ideas to help me investigate this further or corrections to be made in my assumptions please feel free to chuck your 2 pence in.

Cheers!
Ben

 

[Aquarius]

It’s been a long time since I’ve worked on vented cylinders, but I always thought it had a fall, rather then a rise. That lack of 450mm will not be helping. Is he just running the tank near dry from pump?

 

[townfanjon]

Pic poor , all vent pipe looks to cock from what I can see

 

[townfanjon]

It’s been a long time since I’ve worked on vented cylinders, but I always thought it had a fall, rather then a rise. That lack of 450mm will not be helping. Is he just running the tank near dry from pump?

Yes always a slight rise

 

[Plumb Tidy]

Yes always a slight rise

yes i always put a fall in the cwsc or header tank maybe that's what your thinking about.

 

[Plumb Tidy]

With the pic the pipe going straight up is the vent pipe. The horizontal pipe is the hot water feed and there is a tee to the shower pump. the 450mm pipe I'm sure is going downwards. I would just like to know if the vent pipe would draw in air somehow when the shower or bath was run or if the downwards slope would contribute to air before i charge the customer for making right the pipework. Im sure this is wrong so im going to make this right anyway but i would like to know the mechanics behind it if this is making the air draw in.

 

[townfanjon]

The vent pipe should not go straight up , it elbows off the top of the cylinder to a tee , top of tee is the vent , bottom is HW draw off , basic stuff this mate .
Put a manufacturers shower pump connection on the top of the cylinder if you alter it .

 

[Plumb Tidy]

Cheers Town of john. I know it should be 450mm from the centre of the cylinder but why would this be drawing in air, city and guilds and the gaffer says this to you but they don't explain why i know parasitic circulation occurs but that's just in-efficiency not much to do with introducing air locks. The shower pump connection i can under stand specially when two showers are running at 12 litres per minute each they are drawing more water than the cistern can produce. Thanks for confirming anyway mate.

 

[John.g]

The 450mm is. strictly speaking, not required, the required height is (4% of the height from the cylinder cold water inlet to the CWST water level or 40mm/meter)+150MM, if the cylinder/CWST distance is 3M then the required height is (40X3)+150 or 270MM. I don't really know why this requirement but 4% is the amount cold water will expand when heated to 100C so maybe a clue in this.
The point you make about the draw off of up to 24 LPM with two showers is a good one as it will cause a problem if the cistern can't keep up with it from the supply to the cistern or from the cistern to the cylinder.

I just include a snapshot of a 14 LPM electric shower with integral pump which shows the correct way to plumb it in, may be of some help.

 

[Plumb Tidy]

Thats great cheers John G. The shower maybe the issue here it may be taking faster than it can fill the cylinder or because of the way it is tee'd in it may be cavitating which is producing air bubbles. I shall investigate further, cheers for all the help.

 

[ShaunCorbs]

Shower pump where’s the s flange

so it’s pulling air from the vent easy way to test

put a bag over the vent in the loft or you can use your hand get someone to turn on the showers that use the pump you will feel it suck

 

[Plumb Tidy]

Nice one Shaun mate that's an idea! The way to correct this if this is true would be to move the vent more than 450mm away from the cylinder and after the slight rise?

If not i would have to put a proper Surrey flange in.

 

[ShaunCorbs]

Needs an s flange or Essex flange with a dip

 

[CP Plumbing]

The shower pump is been installed the wrong way. They should have used an essex flange.