FE tank overflowing

[ukal]

Hi,

I am having trouble with my Feed & Expansion tank (smaller tank) in the loft overflowing constantly and water continually pouring out of the overflow pipe into the garden.

(this is off the back of this post, but the cause is not the valve //www.diynot.com/forums/plumbing/header-tank-waste-exit-pipe-leaking.324970/#2410678).

I have narrowed it down to the expansion pipe that feeds into the tank from above causing the overflowing. The water seems to be dumped out a couple of minutes after the heating has gone off (not a constant drip).

I placed a bucket under this and with the heating having been on for 3 hours (2 consecutively) the bucket caught approx 3/4 litre of water. This would be more than enough to cause the overflow. Any idea why this much water is coming from the expansion pipe (and I presume coming from the immersion tank)?

Things I have tried (thanks to this forum):

1) changed the ballvalve on the tank (I first thought this was leaking).
2) lowered the speed on my Celsia pump from 3 to 2.

Could there be a problem with the tank or coil itself?

Setup:

FE tank in loft above immersion tank in bathroom.
Large cold water tank above FE tank in loft.
Gas boiler.
The bend in the expansion pipe sits approx 23 inches from tank water level.

Any ideas would be much appreciated.

thanks alot.

 

[Agile]

The filling level in the tank should only be about 100mm deep.

It sounds as if you have it set too high!

Tony

 

[ukal]

Tony, even if I were to lower the tanks water level the water from the expansion pipe would still cause it to overflow?

 

[Agile]

Its the same water being pumped over.

The only way new water is going to be introduced is in the rare case of a part leaking and this would probably need an experienced plumber to identify.

Tie up or turn off ball valve and the level should remain constant.

Regardless you have a pipe blockage or other problem causing the pumping over. That needs to be fixed!

Tony

 

[ukal]

thanks Tony, I see what you mean about it being the same water being pumped over, and tying the ball valve up would stop the over flow.

But as you say, I ideally need to know what possible causes there are for the pumping over?

 

[Agile]

You dont just need to know the possible causes.

You need to get it sorted very quickly before pin holes appear in the rads!

 

[ukal]

what could cause the pin holes in this case? The same blocked pipe causing the pump over possibly?

cheers

 

[Sparkgap]

what could cause the pin holes in this case? The same blocked pipe causing the pump over possibly?

cheers

Circulating water through the tank introduces oxygen into the water = corrosion = leaks eventually.
F&E tank lower than the cold water tank? Sometimes an overflowing tank is a sign of a leak in the coil of the cylinder.
Is the F&E tank correctly sized for the heating system? If the system has been extended there will be more water in it = more volume needed for expansion.
Where does the feed and vent connect to the system? Normally cold feed into boiler return, vent off boiler flow. With a gravity system these connections tend to be made onto the primaries to the cylinder. Then somebody changes it to a pumped system and you get pumping over.
One thing I have seen in the past (though not common) is air in the system causing a surge of water out of the vent: pump starts up and compresses air in radiator, lowers water level in F&E tank which is made up by ballvalve. When pump stops air pushes water out into tank either up cold feed or via vent pipe. Depends on how the pipework and pump is arranged.

 

[ukal]

thanks Sparkgap.

Is the F&E tank correctly sized for the heating system? If the system has been extended there will be more water in it = more volume needed for expansion.
Where does the feed and vent connect to the system? Normally cold feed into boiler return, vent off boiler flow. With a gravity system these connections tend to be made onto the primaries to the cylinder. Then somebody changes it to a pumped system and you get pumping over.

The system has never been extended so I presume the F&E tank is correctly sized.

it looks like the feed pipe from the header tanks goes to the pump next to the immersion tank. It then looks like it goes to the boiler. The expansion pipe looks to run beside this pipe with a junction joining to it. The expansion pipe then carries on down under the floorboards.

One thing I have seen in the past (though not common) is air in the system causing a surge of water out of the vent: pump starts up and compresses air in radiator, lowers water level in F&E tank which is made up by ballvalve. When pump stops air pushes water out into tank either up cold feed or via vent pipe. Depends on how the pipework and pump is arranged.

The symptoms you describe here sound similar to my problem but I dont think the water level drops whilst the pump is on. It drops when heating goes off, water level fills from ball valve then a few mins later a dump of water from the expansion pipe.

One thing I'm going to try is lowering the thermostat temp on the boiler. This could be too high causing all of this water expansion hence the pumping over?