Overflowing F&E tank

[JohnAR]

I have a gas fire CH system incorporating a gravity fed HW circuit with my F&E tank located in the loft above the main water storage tanks.

The level in the F&E tank keeps increasing over a period of roughly 2 weeks (could be shorter) at which point it overflows. The water in the F&E tank appears to be cold on inspection. My first suspicion was a leaky ballcock but although there is the slowest of drips it seams unlikely that this would be the cause also yesterday evening there had been a relatively substantial discharge unlikely if caused by drip. I assume that as the water level in my storage tanks is below the F&E tank it can't be a split coil in the HW cylinder.

I also thought the source might be from the expansion pipe but surely as it is all part of the same circuit water discharging wouldn't increase the level in the tank?

Any ideas please

 

[kevplumb]

isolate the water supply to the tank

then drain it and see if it refills

 

[JohnAR]

I tried this earlier today.

Unfortunately the feed from the cylinder is at the top so when you have stoped any water feeding into the cylinder there is no pressure to force the water out. Therefore when you run the hot taps you get very little water (just what is in the pipes) before they stop running.

I guess I could drain the tank down but the drain valve is very difficult if not impossible to get to.

 

[kevplumb]

part drain the f&e tank with the water supply off and see if the level rises

you could syphon it out with a hose

 

[JohnAR]

I guess if I tie the ballcock up that would be sufficient otherwise my mains could be off for a while.

I will try the above and come back when I have an answer. Out of interest if it does continue to fill up (ie it isn't the drip from the ballcock) what do you think the likely cause might be

 

[kevplumb]

split coil in the cylinder

 

[JohnAR]

I've just had a look and realised that even if I tie up the ballcock the drip doesn't stop. I might have to have the mains off for days to see if it makes a difference not practical I'm afraid

If it is a split coil shouldn't my cold water storage tanks, which are mounted below the F&E tank be trying to equalise their level with the F&E tank, they seem to be fine.

Although, I had added Fernox to the system about 18months ago after it was last drained down to replace a motorised valve and there seems to be little of the very obvious Fernox smell from the water in the F&E tank (possibly being dilluted if coil split).

It sounds as if I might need to get a professional to look at it

 

[brumylad]

try bleeding the rads. Air expands considerably when heated and this might be pushing the water out of your CH system.

 

[kevplumb]

I've just had a look and realised that even if I tie up the ballcock the drip doesn't stop. I might have to have the mains off for days to see if it makes a difference not practical I'm afraid icon_sad.gif

turn the water off and fit an isolating valve in the pipe to the tank and renew the ballvalve

then leave the isolater turned off

 

[JohnAR]

Thanks Brumylad, but I have tried that, all the rads appear to be fine.

Also if it was air caught in the system expanding then I guess you would expect the water in the F&E tank to be hot or at least warm when it is up to the overflow but apart from one occasion (see below) the water is always cold.

As an aside this problem started when I was up in the loft storing some stuff and happened to look in the F&E tank only to find the water was at the very top of the tank under its polystyrene cover. I drained the water down with a hosepipe, unclear as to why it hadn't simply poured out the overflow. Only on closer inspection did I realise that the guy who had owned the house before us had blocked up the overflow with a cork

I removed the cork of course and have had the periodic discharge from the overflow since (at least it doesn't pour into the loft).

 

[JohnAR]

Thanks kevplumb, a bit slow of me there.

I have a friendly local corgi engineer who has done some work for us in the past and have given him a call to come and have a look.