0

so I have a normal non combi boiler and in my loft a cold water tank, then in my airing cupboard I have a hot water tank with an overflow/pressure release pipe that runs up and to the cold water tank for when the water expands (the hot tank is fed from the cold water tank).

The other day I got a call from the neighbour saying my overflow pipe was gushing, and it was really going for it, not just a trickle but like there was a tap on directly connected to the outside!

Wife came home and turned off the mains water and I came home soon as I could a couple hours later to take a look. I looked at the water tank in the loft and the level was a good 4-5 inches up past the overflow pipe! I ran the water for a while to get the water level to drop, turned on mains again and it refilled without any issues... Hasn't happened since, as yet...

I cannot for the life of me work out how this might have occurred, the only thing I can think of is that the water mains pressure was somehow so high that it forced past the float valve somehow?

I noticed that the hot water tank was also cold, I didn't check at the time but there's a chance the water had risen so high it had started pouring into the hot water tank from the hot tank outlet possibly, but I don't think it's related to how the cold water tank got full in the first place...

Anyone ever had anything like this? Could the valve just had seated a bit dodgy and not sealed off properly perhaps? If so how could I check this, it seems fine now checked it earlier today and at most there is a very irregular tiny drop coming from it that's it...

  • The hot tank outlet (by which you mean the hot tank overflow outlet I presume) typically forms an inverted U over the edge of the cold water tank. There is no way for cold water to flow up the U and down into the cold water tank. Even if the hw overflow comes into the side of the cold tank, I still don't think much cold water could get into the hw tank; it is already full of hw, and although the cold is denser, the difference isn't that big. – Martin Bonner supports Monica Oct 24 at 12:43
  • Check the float valve, probably the float isn't air-tight any more and water entered it. Also add a pressure regulator to tank cold inlet: in the future, even in case of pressure spike, you will be safe. – DDS Oct 24 at 13:37
  • @MartinBonner yeah I wasn't really sure that was a possibility, still not got a clue what caused it – MorkPork Oct 25 at 14:11
  • @DDS I wondered about the float but once I dropped the water level back down it seems to be working fine (it was also up as high as it could be when I checked the tank initially and had shut off the water, it was just 5 inches under the surface) and when I checked it the next day it still appears to be ok – MorkPork Oct 25 at 14:12
0

If you have a shower mixer that lets through it is possible for mains pressure cold water to backflow through the mixer and into the hot water tank system.

  • I wondered about that but our shower is fed from the cold and hot water tanks and there is pump to up the pressure so I'm assuming it's not that 🤔 – MorkPork Oct 25 at 14:10

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.