What overflows into our cold tank?

July 19, 2005 5:22 PM

What overflows into the cold water tank in our loft? The tank overflowed itself because water was pouring into it from an overflow pipe. This continued for many minutes, until I turned the main stopcock off. It has never happened before.

The mystery pipe is _not_ the mains inlet pipe controlled by the ballcock, nor is it the central heating circuit expansion pipe. It appears to come up from the garage where the hot water tank and boiler are. I can only guess that it is the expansion pipe for the hot water, but expansion pipes don't gush, they dribble surely? This was gushing cold water under enough pressure that I couldn't stop the flow with my thumb.

Sadly (and incidentally) squirrels had eaten the overflow pipe from the cold tank! So that overflowed into the loft, down through the bathroom and into the garage. Luckily we've had some nice hot weather to dry everything out.

posted by denishowe to home & garden (2 comments total)

If you have a cold water tank in your loft connected to a hot water service in the garage, it sounds to me like your hot water service is not a mains-pressure type, that the cold water tank is actually what supplies it, and that the pipe connecting the two is the cold water supply from the cold water tank to the inlet of your hot water service.

If you've got water flowing backwards up that pipe and it stops when you turn off the main stopcock, it sounds like you've got mains pressure cold water finding its way back into the hot water service's hot water outlet.

This can happen if you've got a mixer faucet somewhere, its outlet is blocked, and both taps are on.

Any help?
posted by flabdablet at 6:43 PM on July 19, 2005

Genius! You may just have cracked it there flabdablet.

At the time the kids had a hose connected to a mixer tap. It's entirely possible that they turned on both taps. The gun on the other end of the hose cuts off the flow unless you pull the trigger. I can believe that high pressure cold water could have forced its way up the hot water expansion pipe. I'll try it next weekend.

I owe you what it would have cost to call a plumber round to fail to explain it :-) Thanks.

Now for those squirrels...
posted by denishowe at 4:50 PM on July 21, 2005