Expansion Tank Overflowing

[biggy461]

I've noticed that my expansion tank is overflowing into the front garden.

I've bailed out the expansion tank and the it doesnt appear to be the float valve.

I have noticed water flowing in from the feed at the bottom of the expansion tank. But this seemed to stop once the water in the cylinder had heated up.

The cylinder header tank is located about 2 feet above the cylinder in the bathroom and the expansion tank a further 2 feet above this. The cylinder header tank is not overflowing.

I believe but praying that its not - that the cylinder coil may have split - but was looking for other ideas first before replacing.

Any thoughts ??

 

[jobloggs]

I think you have put your finger on the problem.

Check as follows for your arrangement.

Tie up the ballcock in your hot water tank.

Drain a few inches of water out of this through your bathroom taps.

Measure the level of the water from top of tank.

Run the boiler on HW setting. (if you have zone valves and a tank stat you will need to either do this when system is cold or turn up the stat a few degrees to create demand for HW).

If coil is split/holed water will flow from it into cylinder and raise the level in the cold storage tank. Check after an hr or so.

Needless to say don't run taps or flush toilet while you are doing all this.

Report back to this forum.

 

[JohnD]

There will be a bit of expansion of the water as it heats up (hence: Feed and Expansion tank) which will be much greater if there is air/gas in the rads that needs bleeding out (it expands a lot more than water).

Adjust the float so that the water level is only about an inch above the F&E pipe so that you have plenty of room for expansion.

And bleed those rads.,

You may have diluted the corrosion inhibitor so when you have fixed the overflow, add another 5 litres of the same chemical that you used before (you did use one before, didn't you?) If there are signs of sediment or corrosion it would benefit from (at least) a chemical clean and flush.

edited to say, Mr Bloggs is right, but if it isn't a leaky coil, try this

 

[biggy461]

Thank you for your replies guys.

If coil is split/holed water will flow from it into cylinder and raise the level in the cold storage tank. Check after an hr or so.

I've just had a thought - correct me if i am wrong - but i dont think it can be the coil now as the cold water storage tank is not overflowing which after reading your posts it would do.

And bleed those rads.,

No air in the rads, i've bled them all and got no air.

The expansion tank is overflowing but ball float appears to be shutting off. I think i may drain down this weekend - replace the expansion tank (full of sh*t) and ball float and see if this resolves the issue.

 

[JohnD]

I've just had a thought - correct me if i am wrong - but i dont think it can be the coil now as the cold water storage tank is not overflowing which after reading your posts it would do.

No, what happens is that the flow through the leak tries to equalise the levels in the cold water tank and the F&E (though the circulating pump adds to the apparent head*).

If the level in your cold water tank* is higher than the overflow in the F&E, it will run out there.

My money's on that cylinder coil now.

 

[jobloggs]

Just clarify something for me.

You talked in your first post about the relative levels of the tanks. Was that the level of the bottom of the tanks or the level of the water in the tanks when the ballcocks close?

If it is the latter then my first reply is incorrect. The head (pressure) in the coil would be greater than in the cylinder even when pump is off and even greater when pump is on. Flow will always be from tank with higher water level to the one with lower water level.

In cases where water levels are similar no exchange will occur when pump is off. When pump is on this will raise pressure in coil but flow into cistern might not cause overflow of cold storage tank if water level at which ballcock closes is well below overflow level. This volume might not be pumped across before taps/toilet flush reduces the level to that of closed ballcock.

Report back please.

 

[biggy461]

You talked in your first post about the relative levels of the tanks. Was that the level of the bottom of the tanks or the level of the water in the tanks when the ballcocks close?.

This is the level of the bottom of the tanks. The expansion tank is in the loft about 2 feet above the cold water storage tank which is in the bathroom about 2 feet above the cylinder.

Flow will always be from tank with higher water level to the one with lower water level.

Will this be true even if the F/E tank is above the cold water storage tank ? The water volume and level is lower in the F/E than in the Cold Water storage tank as the F/E is smaller.

 

[JPC]

its the water level u need to check.

if ur f and e is higher (it shouldn't be ) if u get a split coil the system efectively becomes one system and the water levels will balance and hence u'll get ch water in ur cwsc. (not nice, and thats why it should be the other way round)

is ur hot water discoloured ?

ur cwsc could also be filling up thru the feed pipe if u have a faulty mixer tap ie monobloc ? shower valve ?
cold water under mains pressure works its way up the hot pipe.

 

[JohnD]

The water volume and level is lower in the F/E than in the Cold Water storage tank as the F/E is smaller.

If you mean that the top of the water is lower in the F&E than in the cold tank, then yes, the water levels will try to equalise through the leak. The pressure of the tank will change the "apparent" head when it is running.

The height of the bottom of the tank is not relevant.

 

[jobloggs]

JohnD wrote

The pressure of the tank will change the "apparent" head when it is running.

I think he meant to typepumpnot tank but he is correct in that the flow thru the split may be slowed or even reversed when the pump is running.

If a HWST is has a lower water level than an F&E tank flow will always be towards the HWST but it may not over flow and be picked op as it is frquently drawn down by taps/flushing. This is undesireable and also as JPC says you are then cleaning your teeth with water from your heating system probably with inhibitor added.

Eventually in both case the heating system water is being lost and replenished with new oxygenated water and inhibitor is being diluted. Corrosion will eventually occur.

Afraid that there is little doubt that you have a holed coil and you need to get this fixed ASAP to avoid corrosion probs in the future. Probably £400-500 depending on type and area.[/b]

 

[biggy461]

Just a quick update to say i replaced both ball cock valves in the F&E and cold water tank - seems to have solved the problem - must have been a slow drip on one the ballcocks

i also took the opportunity to add some TRVs to the rads throughout the house.

anyway - thanks for all you advice