Attic tank overflow

[defblade]

We've got 2 tanks in the attic, so a system basically like this:



Tonight the overflow (which is branched to both tanks inside) was running quite freely when I got home - not gallons, but a lot more than drips.
I expected, once again, to have to change the washer on the bigger one's ball valve, but actually it was the little one overflowing, and the ball valve was fine.

So I guess the expansion pipe that sits over the top must have been putting out a fair volume of water just as I came home - it gave a little spit while I was up there - but filling enough to overflow (without the ball valve leaking) is new behaviour for the small tank - it normally sits well below the overflow and hasn't done this before (as far as I've noticed...) in the 16 years we've been here.

Heating and hot water both seem to be doing what they should from limited checks this evening.

Should I be worried, and if so, what should I be checking?

[Richard-D]

I've had this. If you Google 'pumping over' you will get a better description than I can provide.

Usually caused by a blockage building up in your pipework near the filling T. You may be able to lower your pump speed as a temporary measure.

[defblade]

Cheers

It's not filling/over filling that quickly, so I think we'll be ringing the plumber next week about either flushing the system, or posibly going sealed after seeing some google comments.
TBF, we've lived here over 16 years and only really serviced the (oil) boiler in that time, we've left the rest alone as much as possible (one sticky zone valve replaced, although I have become an expert at fixing those bloody Drayton actuators....)

[Sheepshanks]

The obvious fault is the coil in the hot water cylinder is letting water from in from the cylinder. Is the big tank refilling as the small one overflows?

If it was pumping over it shouldn’t overflow as the same tank replaces the water so it just goes round in circles.

[LooneyTunes]

defblade said:

I think we'll be ringing the plumber next week about either flushing the system, or posibly going sealed after seeing some google comments.

My suggestion would be unvented system or combi boiler depending on the size of the house. Loft mounted tanks have caused us way more problems than either of those. Not usually overly complex to change them, assuming of course that in the case of an unvented you've got space.

[defblade]

Sheepshanks said:

The obvious fault is the coil in the hot water cylinder is letting water from in from the cylinder. Is the big tank refilling as the small one overflows?

If it was pumping over it shouldn’t overflow as the same tank replaces the water so it just goes round in circles.

I'm really not sure what's going on exactly. As I came home from work Thursday evening, the overflow was running but even as I was getting the ladder out to get up there, the flow settled to a trickle then drops. While I was up there mostly fiddling with the ball valve I had a small splutter from the vent pipe (which I've not seen before, but then I don't spend a lot of time sitting in the attic watching them!) but I was bailing water down the overflow (via a flexi-funnel) and then adding water from the big tank to test the ball valve, so I don't know if either tank would have been filling with fresh water at any time by itself.

There's been no wet patches under the overflow in since Thursday evening; I'll have to get back in to the attic to see if the small tank is slowly filling back up, not to the overflow yet, but that'll probably have to be tomorrow as we're out today.

[Sheepshanks]

I’ve had pumping over before - after we had a new pump fitted - and as the system starts the water level in the little tank drops and water comes out of the top (vent) pipe. Thinking about it, I suppose if the level dropped enough to open the float valve to let more water in, then it might overflow as the pump went off and the water level returned to normal.

All I had to do in our case was slow the pump down and drop the water level a bit in the CH header tank - it was very full. The vent pipe wasn’t really high enough, it only just skimmed the top of the tank.

If it was the cylinder hot water coil I’d think that one it went it would let water in all the time, it wouldn’t be intermittent.

[defblade]

I went back up to look on Sunday... and the ball valve was dripping, and it had filled an inch or so.
Only just had time to fix that today - the water was another inch or so higher, a little below the overflow.

I'll keep an eye on the levels in a few days again, but I now think that catching it running over was a combination of the valve dripping bringing it up to the pipe and then a bit of a vent spit which would normally not be noticed as the level is a long way down and it would be pulled back into the system again anyway causing the brief running overflow.

Might be a good hint to get the system gently cleaned though.