Trickle Of Water From F&E Vent - Is Pipe Layout Wrong?

[senator3litre]

Please excuse my Rolf Harris type diagram (can you tell what it is yet kids?). My brother's vent pipe has a constant trickle of hot water into the F&E tank when the system is on. I'm not sure how long this has been going on - poss. years. Everything works fine.

The pipe rises on a diagonal from where it comes through loft floor, then just rests on the edge of the tank. The vent pipe in my house rises vertically, and curves over like a 'shepherds crook'.

Is the vent pipe the problem, or is there another reason(s)?

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• senator3litre
• 1 Mar 2009
• 1

 

[Bambergaspipe]

How many F&E tanks have you got.? 2?

 

[JohnD]

there can be various causes, but in the tank with the sloping vent, there is very little extra height for the water to rise before being pumped over, yours is correct with the rise and bend.

Things to do:
1) check the pump is at low speed
2) adjust the ball valve so that depth of water in the tank is only a couple of inches above the outlet

(these are both quick and easy)

3) do a bit of piping to raise the vent pipe so that it has a bend a couple of feet above the water level, and then coming down through the lid on the tank

As it has been pumping over for some time, it is likely to have a lot of corrosion and sediment in the system, you can give this a simple chemical clean and flush (I like Sentinel X400 which you should do before the end of the heating season, since it ought to be circulated hot for 4 weeks before draining and rinsing.

I am a householder not a pro

How many F&E tanks have you got.? 2?

There is one in his house and one in his brothers

 

[D_Hailsham]

To BG

How many F&E tanks have you got.? 2?

Read the OP's post!

My brother's vent pipe has a constant trickle of hot water into the F&E tank when the system is on.

The pipe rises on a diagonal from where it comes through loft floor, then just rests on the edge of the tank. The vent pipe in my house rises vertically, and curves over like a 'shepherds crook'.

The two sketches are also clearly labelled "Brothers (problem) tank" and "my tank".

To the OP

The problem is that your brothers vent pipe does not rise far enough above the water level in the tank before it bends over. The distance between water level and the top of the bend should be at least 400mm.

 

[Bambergaspipe]

The problem is that your brothers vent pipe does not rise far enough above the water level in the tank before it bends over. The distance between water level and the top of the bend should be at least 400mm

Really, load of old Bollo*x your system is overheating somewhere, may be sludge build up, how old is the system, may need flushing

 

[D_Hailsham]

The problem is that your brothers vent pipe does not rise far enough above the water level in the tank before it bends over. The distance between water level and the top of the bend should be at least 400mm

Really, load of old Bollo*x

Really?????

This is from the Vaillant Installation manual:

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• D_Hailsham
• 2 Mar 2009
• 2

It is possible to have the pipe sloping, provided the length from the water level in the tank to the top of the bend is still 400-450mm.

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• D_Hailsham
• 2 Mar 2009
• 1

 

[senator3litre]

Thanks for the replies so far.

D_Hailsham - The length of the vent pipe from floor to tank is about right, but it doesn't rise at such a steep angle as the one in the Vailant manual that you included. Also, the pipe rests on the lip of the tank, your is some way above the tank.

Bambergaspipe - Yes the system is ancient (Ti Fuelsaver gas boiler), but works perfectly. Where is the most likely place for a partial blockage?

 

[Bambergaspipe]

Bambergaspipe - Yes the system is ancient (Ti Fuelsaver gas boiler), but works perfectly. Where is the most likely place for a partial blockage

If it`s sludged up which it most likely is, it will more than likely be in radiators, will need a good flush. you can do this yourself don`t bother with a powerflush it`s pointless and useless.

 

[LeedsPlumber]

Bambergaspipe, maybe you should keep your 'opinions' to yourself as that is all they seem to be, and stop giving wrong/ misleading information, seems that what you have to say on most posts including this one, is its rarely based on fact and in most cases is fiction from one of the superman comics you subscribe to.

 

[D_Hailsham]

D_Hailsham - The length of the vent pipe from floor to tank is about right, but it doesn't rise at such a steep angle as the one in the Vailant manual that you included. Also, the pipe rests on the lip of the tank, yours is some way above the tank.

It's not the length of pipe from the floor but the length of pipe above the water level which is important; this is clear from both diagrams.

When the water is cold, the level in the vent pipe will be exactly the same as in the F/E tank. When the water is heated, the level in the tank will rise due to expansion, but the level in the vent pipe will rise further because the pressure in the vent pipe will be higher than that in the cold water feed pipe. If the vent pipe is not long enough you will get pumping over.

This problem is reduced by ensuring that the connections of the vent and cold water feed pipes to the flow pipe are no more than 150mm apart. Ideally the flow pipe should be horizontal with the vent and cold feed rising from it - the cold feed can be connect in a inverted loop as in the Vaillant diagram; this prevents air bubbles rising up the cold feed pipe.