Immersion tank giving hot water over days long period

Emmy23

Hi, 

My partner and I have just moved into a rented house and we're a bit confused by something that's happening with the immersion heater. We have been turning the hot water on for approximately 30-40 minutes via the control panel under the boiler before using it. We tested to see if we still had hot water the next day and we did, so used it. This has now been going on for 3 days and we haven't had to turn the water on via the control panel once. We are worried because we are unfamiliar with this system, having only had combi boilers, and don't think we should have been having hot water for this long without having to turn it on again. We think there might be a fault and we'll get charged more for electricity. 

The control panel (made by Potterton) is in the kitchen under the boiler (Vaillant ecotec plus 418). We looked at the boiler and it only seems to set the heat of the water, and the tank itself is in our bedroom cupboard on 3rd floor (Range Tribune tank). 

Any advice anyone can give would be greatly appreciated. We don't know much about the system itself and everything we've looked at online is a bit confusing. 

Thank you

macman

Since you have a conventional boiler and a hot tank, the assumption is that the boiler provides both the CH and the DHW too, as that is much more economic. The immersion heater is either there as a backup in case of boiler failure, or it predated the boiler install. You should have a way of setting the timing up for the boiler to heat the hot water tank, either from the boiler controls, or on a separate programmer.
Suggest you post a pic of the control panel and boiler.
Or you could just ask your LL to explain the system?

nofoollikeold

1. Your's is a "regular" boiler, which will almost certainly provide:
1a. Hot water to heat the water in your hot water cylinder (HWC).
1b. Hot water to heat your radiators and / or underfloor heating (space heating).
2. It is not a combi boiler, and does not provide hot water on demand.
3. The control panel, or programmer, will probably allow you to set times for space heating and water heating.  You should be able to set it to space heating, or hot water, or both, or neither.
4. The hot water cylinder you have is what is known as an unvented hot water cylinder.  The water inside it (which you use for washing etc.) can be heated:
4a. By hot water from the boiler.  This hot water (the "primary" water) runs through a coil of copper pipe inside your HWC and heats the water you use by conduction through the pipe.  The hot water you use never itself goes through the boiler, it is heated indirectly.
4b. By one or more electrical immersion heaters, one about 1/2 up from the bottom of the HWC, the other nearer the top.  These immersion heaters will have thick, normally white, electrical cables running to them from some form of outlet, usually wall mounted and with a switch.  Their may be other cables  - don't confuse them.
5. While the HWC is being heated indirectly by the boiler, a thermostat monitors the temperature of the hot water you use.  When it reaches a pre-determined value (normally around 60 degrees), the thermostat causes a motorised valve to shut, which in turn will turn the boiler off (unless space heating is happening at the same time).  
6. While the water is being heated directly by either or both immersion heaters, again a thermostat within each heater will determine when the water has reached a pre-determined value, and will then cut off the electricity to the heater(s).  When the water cools, electricity will once again flow to re-heat the water.
7. Modern HWCs are very well insulated, and may well keep water hot for many hours without using additional energy.  
8. I would suggest you do the following:
8a. Check the cylinder for immersion heaters, and if it has them, turn them off at the wall outlets.  As electricity is roughly three times the price of gas, its an expensive form of heat.
8b. Set the programmer to run the boiler for hot water for an hour a day, say 06:00 to 07:00 to provide for morning showers.  If you run out of hot water, set it for a further period, perhaps 16:00 to 16:30 to provide evening hot water.