noisy hot water tank when boiler not on

thriftytiger

Hi, I wonder if anyone can help. We recently moved into a new house with an old style gas boiler, central heating, hot water tank system. The boiler is in the kitchen, the hot water tank in a bedroom, and cold water tank in the attic. The hot water and heating are controlled by a honeywell panel and thermostat in the kitchen and are set to come on for a few hours morning and evening. The problem is that the hot water tank (or something in the cupboard with it) seems to 'start up' and makes a lot of noise in the middle of the night eg. 3am when the boiler is not on. There are two electrical switches on the wall next to the tank. I presume one is to power the pump etc, and the other we think is for the pump for the shower (which also uses water from the tank). Does anyone know why it is coming on in the night and what we can do about it?
It is so noisy it wakes people up if they sleep in the room.
many thanks!

notbritishgas

About how long does this noise last for?

thriftytiger

I'm afraid I'm not sure. It doesn't wake us from our room, but I've heard it when getting up in the night to go to the loo etc and have been in to have a look. If I had to hazard a guess I would say at least 15 mins, but I'm usually back to sleep after that time so can't be sure.

alleycat`

First question is where does the boiler live?

It will have a frost protection stat so it might come on if the temperature is below a certain threshold.

It could also be that the shower pump is surging due to a change in water pressure / back feeding at that time of night.
It should (and sounds like it does) have an isolation switch.
Turn the power off on that and see if the problem goes away.

On the central heating system you've described the mostly likely culprits for noise are the pump and the motorised valve.

--
The pump will look something like this:-

http://lh3.googleusercontent.com/public/FnVKaUGPB36E2owm4o-UmqWEIFUe4DfI5V99BpCByhEch9Sd5Rzf1FPCdiv-3jOV0xEiC6Rv_R2MP33gEyB2UYIvlIodavCHbohL6wJeIAnzHONJGpKtvMK53ppGHoRsVKGt6ZGaQn3Ax6i_CKpgnb-vl-HeNTUiQgzrQOkMXDb6_lMYflXqFdb76qt-xLkeGVUP36QcP0tw

It usually has a 3 speed impeller.
This can seize up if the system has not been cleaned in a while and debris gets stuck inside it.
Usually it'll make an awful whining noise.
--

The motorised valve will look something like this:-

http://www-3.plumbworld.co.uk/salus-22mm-2-port-motorised-valve-00017053L.jpg

Likewise if the valve gets debris inside it it can stick/whine when it is moving from hot water to central heating and back.

They usually have a manual override "slider" on the side that you can manually force backwards and forwards to see if it is stuck.

--

I suspect the shower pump surging is the culprit (assuming you are right about when the boiler kicks in).
So my first choice would be to turn that off and see if the problem goes away over night.

rogerblack

Is the noise like a kettle or a pan boiling?

penrhyn

Assuming the central heating is off, I'd suspect its an immersion heater running off a timer, using economy 7.

thriftytiger

Thanks Alleycat, will try those things. - the boiler is in the kitchen and I don't think it has been particularly cold on the nights I've heard it, although I read somewhere these can kick in at 4 degrees so might be a possibility. Have wondered about the shower pump thing.

rogerblack - yes it does sound like boiling water. One of our guests said they thought it was someone having a shower.

thriftytiger

I've thought about an immersion heater but there is only one tank, could an immersion tank be within this tank? Also we do run out of water after a couple of baths/showers but ofcourse this is during the daytime. Would there be a switch for an immersion heater and/or economy7?

penrhyn

Examine your hot water tank, has it got a cable going to it?



2 Cold Water in
7 hot water out
5 hot water heating coil from central heating
6 Electric immersion heater.

macman

thriftytiger wrote: »

I've thought about an immersion heater but there is only one tank, could an immersion tank be within this tank? Also we do run out of water after a couple of baths/showers but ofcourse this is during the daytime. Would there be a switch for an immersion heater and/or economy7?

An immersion heater is inside the hot water tank-that's why it's immersed.
If it is on 24/7, switch it off, as it's going to cost you a fortune.
I suggest you set your alarm for 3am, get up and properly identify where the noise is coming from.

rogerblack

The noise can be due to the element getting lots of scale on it. Replacing it may fix.
Are you in an area which is very prone to scale?