Electric immersion water heater - timer question

[drsabrown]

Hi, I've moved into a house where the primary hot water supply is a gas boiler and hot water tank. However, there is also an ensuite in the attic that is supplied by an Ariston Classico unvented electric immersion heater (model STD 125). The tank has 2 immersion heaters, one at the bottom and one at the top and according to the manual, the bottom one is for night time and the top one for a day time top up. I understand this is typically for use with Economy 7 tariff. Each immersion heater is wired to a separate mains switch.

The previous owner told us that in order to get hot water we should turn on both immersion heaters for a few hours. This all works fine, however, it is not that convenient to turn the water on an off manually each day. Is it advisable to put a timer switch that will turn on both heaters for a couple of hours each morning? Or separate timer switches for the two heaters?

Any advice on a simple setup would be much appreciated. btw, we're not on economy 7.

Thanks and regards,

Simon

[Rumble]

Immersion heater timers are generally hard-wired downstream of the switch.

You will most likely need one timer per immersion heater, because the timer will not be rated to switch the power of two heating elements.

In a couple of hours, the lower heater should heat your tank on its own I would have thought, so you may wish to put the lower heater on a regular timer and have a 1 hour boost timer (e.g. Horstmann E30.) for the top heater,

[drsabrown]

Many thanks for that - makes sense. I'll probably put a timer switch on each, have the night one come on for a couple of hours and then the day one come on for 15 mins in the morning before i use the shower.

Cheers,

Sim> [e-mail] wrote:

[David Hansen]

On Tue, 8 Jan 2008 01:36:00 -0800 (PST) someone who may be [e-mail] wrote this:-

That is the case. The bottom one would come on automatically at off-peak periods to warm the whole cylinder. The (expensive) top one would be switched on as necessary to top up the cylinder temperature.

The top one should be adequate to heat enough water for a shower and general washing. If it isn't then perhaps you spend too long in the shower and are using as much water as a bath would:-)

Personally, as a first stage, I would put a timer on the top immersion heater. Models are available which replace an existing switch. I would ignore the bottom heater. This can be set depending on usage, for example on all day or on twice a day as appropriate.

After that I would consider the options. Why does the en-suite have a separate storage system as opposed to being connected to the main storage? Unless there are long pipe runs due to a badly designed room layout few houses are big enough to warrant more than one source of hot water.

Depending on the answer to this there would be many options for a more permanent solution, depending on inclination and circumstances.

One idea that might fit some situations is to fit a retrofit heater battery in place of the lower immersion heater. This could take hot water from the boiler or a solar panel. Such heaters are not ideal due to their low surface area, but they avoid the disruption of a new cylinder.

Then heating up the whole cylinder with the bottom immersion heater will be expensive. I would avoid using it.

[drsabrown]

That's really useful - thanks very much. This looks like a simple replacement for the switch on the top heater:

agree about the need for a second boiler for the ensuite - I don't know why they went down that route. We moved from a flat that had a basic combi boiler for heating and HW to this house with a hot water tank, cold water tank and a second immersion heater etc. Before we actually moved in we thought we'd replace it all with a combi boiler, however, it all works really well and has been carefully maintained and serviced - so for now we're going to change as little as possible!

Many thanks,

Sim> On Tue, 8 Jan 2008 01:36:00 -0800 (PST) someone who may be

[David Hansen]

On Tue, 8 Jan 2008 06:13:24 -0800 (PST) someone who may be [e-mail] wrote this:-

with a separation of at least 3mm. If not then a separate switch should be provided to isolate the heater. This can often be done by placing the clock in the kitchen, where there is often a second switch controlling top-up and leaving the switch by the heater alone. This may not be possible in your case, in which case I would probably install the clock as a replacement for the existing switch and mount it alongside with a little new cable to link the two.

Why? They can have advantages in small flats, but have few advantages in larger places.

Then I would just consider a replacement heater battery for the lower immersion heater, in order to reduce electricity bills.

[drsabrown]

Thanks again. So there's a timer switch, then an isolating switch (i.e. the existing switch) and then the heater? Just looking at the guide for the appliance and that seems to be what they suggest also.

Regarding combi boilers - that was just our lack of experience - we're much happier with what we have now. Offtopic - when our boiler eventually dies, can we basically keep this system and get a replacement boiler (presumably condensing?)

Cheers,

Sim> On Tue, 8 Jan 2008 06:13:24 -0800 (PST) someone who may be

[David Hansen]

On Tue, 8 Jan 2008 06:47:55 -0800 (PST) someone who may be [e-mail] wrote this:-

That's what I would do, with the timeclock where the current switch is and a new short length of suitable cable between the two.

That assumes the existing cable cannot be pulled out enough to install the clock without disturbing the switch.

Yes. However, I would use the upheaval as an excuse for modifying the system along the lines I have suggested. I would also go for a heater battery replacing the lower immersion heater, perhaps in the spring.

does one for £105, though it would also need controls and pipework to the existing system.

[drsabrown]