constant hot water when boiler and immersion switched off?

[rkd]

Hi,
I'm very confused as to what is happening with my hot water. For months now I've had this banging noise in the pipes, or what sounds like the pipes but nobody has been able to locate where it's coming from. It happens when my immersion heater, my boiler and washing machine are all switched off, so we just can't figure it out. In the last couple of weeks (since the boiler got serviced) I have also noticed that we seem on certain days to have boiling hot water, even though the boiler is switched off and the immersion heater is switched off and they have both been off for a day. I do have my washing machine on but I didn't think would affect the tap water? Also there is a pipe which runs from upstairs where the immersion heater is, down into my kitchen which always seems to be hot. I suspect (!!) this is where the hot water is coming from. Do you think my immersion heater might be broken? Why is the water hot when it is actually switched off? I am so confused and the plumber I had around said he couldn't work it out either! Any help would be very, very much appreciated!!!

[plumbbob]

Lets start with the banging noise. Do you get just a single bang on its own then silence or are there loads of bangs together with a fizzing type noise?

When you say "boiling hot water" do you really mean burn your hand boiling hot or just pretty hot?

How much hot water is there when the boiler is off? If the tap is run say for 30 seconds is it still hot?

Check the large header tank in the loft. Is the water there above the ambient air temperature?

[rkd]

Hi there, thanks for replying. There is either one loud bang or two consecutively. I can't hear a fizzing noise. The water is very hot in that I can't keep my hand under it. What I've noticed now is that this pipe which I mentioned was hot, begins as cold and when you put the tap on it then becomes very hot as does the water. Yet the immersion heater and boiler and totally off (infact I unplugged the boiler plug completely). If you run for 30 seconds yes it is still hot, I let it run for a few minutes and it seemed to get hotter and hotter.
In the loft all we have is a small black box exactly the size of those small recycling black boxes. I think maybe it's for overflow (?) as there is not much water in it at all. It certainly couldn't be a water supply. The immersion heater in the bathroom is constantly making slight noise though, as thought it is working even though the switch is off. It seemed to work fine the last couple of years though. We did have some work done on it lately, as it kept constantly overflowing out the overflow pipe causing the outside house wall to be damp. I'm not sure if that is related. I hope that helps. If there's anything else you need to know please ask.

[ally]

sounds like the switch for the immersion heater is faulty (ie always on)
Isolate the heater at the fuse box to prove this.The noisy pipes are caused by "water hammer".Draining down the system sometimes cures it.
To do this, first switch off immerser and boiler. Then close the main water stop cock. open all cold taps (downstairs and upstairs). When water stops running close all taps and then open main stop cock. Don't ignore/put up with this noise as vibrating pipes may eventually crack.