Controlling immersion from two cylinder stats

[88v8]

In our present house we have gas heating. On the HW cylinder I have two stats, one near the top of the cylinder, one nearer the bottom, selected by a changeover switch. This gives the option of heating a full tank, or less water if no one is having a bath. This has worked well for 28 years.

In our next house we are all-electric. I would like to fit the same dual stat arrangement to control an immersion. Am I right in thinking that I will need a relay, or are there stats that will switch the immersion direct?

Ivor

 

[dcawkwell]

In our present house we have gas heating. On the HW cylinder I have two stats, one near the top of the cylinder, one nearer the bottom, selected by a changeover switch. This gives the option of heating a full tank, or less water if no one is having a bath. This has worked well for 28 years.

In our next house we are all-electric. I would like to fit the same dual stat arrangement to control an immersion. Am I right in thinking that I will need a relay, or are there stats that will switch the immersion direct?

Ivor

No simply two switches. Switch one connected to top thermostat and the immersion heater will heat the water until the top thermostat cuts it off.
Switch two connected to bottom thermostat and the immersion heating.

If you want only part of a tank switch one on and it will heat only top of tank.
If you want all tank switch two on. It doesn't matter the position
of switch one as switch two will heat the tank until the whole cylinder is hot.

 

[xr4x4]

In our present house we have gas heating. On the HW cylinder I have two stats, one near the top of the cylinder, one nearer the bottom, selected by a changeover switch. This gives the option of heating a full tank, or less water if no one is having a bath. This has worked well for 28 years.

In our next house we are all-electric. I would like to fit the same dual stat arrangement to control an immersion. Am I right in thinking that I will need a relay, or are there stats that will switch the immersion direct?

Ivor

No simply two switches. Switch one connected to top thermostat and the immersion heater will heat the water until the top thermostat cuts it off.
Switch two connected to bottom thermostat and the immersion heating.

If you want only part of a tank switch one on and it will heat only top of tank.
If you want all tank switch two on. It doesn't matter the position
of switch one as switch two will heat the tank until the whole cylinder is hot.

I guess you could take it a stage further by putting two timers, one on each immersion element.

 

[Norcon]

and it will heat only top of tank

If the immersion is located at the bottom how does it heat only the top of the tank? By the time the stat kicks in the lower section will also have been heated to a degree.
OSO fit two immersions whereby you can energise the middle one or the lower immersion separately.

 

[OwainDIYer]

electric immersions have thermostats inside them so you wouldn't use strap-on cylinder stats.

If it's all-electric the house is quite likely to have Economy 7 and you will have a controller like this

which operates the bottom (bath) element overnight and lets you boost the top (sink) element during the day, without leaving it on by accident.

 

[88v8]

Thankyou all. Many ways to skin the cat, it seems.

We do have Economy 7, but no controller, just a (broken) time switch in the airing cupboard and only one top-loading immersion in a 48" tank. Well, the plumbing dates back to 1969... The main Sangamo timer is intelligently positioned in an outhouse, in a high cupboard with no lighting, doh...

Yes, I'll have to get used to taking a bath in the morning instead of the evening; the storage rad that heats the bathroom - at least I hope it does - will be pretty chilly by evening I suppose, and there isn't space in the bathroom for an open fire like we have in our present house.

I'm not sure I can just switch the stats separately, well I could but I think it will have the same problem as using a double-pole switch to change over, the problem is it will fry the stat contacts, because all the tank stats I've looked at are rated 4/6A or less. This is why I think I'd need a relay, which in fact I already have in my electrical museum.

It's true the immersion will heat at the bottom as well as the top, just as the boiler does on an indirect system, but the hot water rises to the top of the tank and so by putting one tank stat near the top one cuts off the heat when the water in the top third of the tank is hot.
This is a worthwhile mod with any gas or oil system, well OK not combi, where there are only two people in the house and the bath is not regularly used. We rarely need to heat the whole tank and it must have saved us a bomb over the 29 years since I fixed up this arrangement. The changeover switch is in the kitchen by the programmer so it's easy to see what's what.

I didn't realise there are tanks available with two immersions. A fact-finding mission to my local plumbers' merchants seems to be required.

A timer for each immersion wouldn't really work in our household, as we also have an electric shower so the bath is used only as an option, perhaps twice a week. All the more reason of course not to heat the whole tank as is happening at the moment.
Also, I think I'd need to avoid overlap between the timers, otherwise the two immersions would be pulling 26A through the main feed ?? Also a point against separate switches ??

Thankyou

Ivor

 

[OwainDIYer]

I didn't realise there are tanks available with two immersions. A fact-finding mission to my local plumbers' merchants seems to be required.....
Also, I think I'd need to avoid overlap between the timers, otherwise the two immersions would be pulling 26A through the main feed ?? Also a point against separate switches ??

You would normally use the bottom heater on Econ 7 and only use the top heater on peak rate. A modern foam insulated cylinder will keep hot for a couple of days if it's big enough. Mains pressure (unvented / 'Megaflo') cost quite a lot more but will give you a mains pressure shower using nice cheap electricity.

The Econ 7 controller shown will work off either two separate circuits (peak and off-peak) or off one circuit and will switch the elements so both can't be on together.

 

[OwainDIYer]

If you are working with Economy 7 you will not have tank stats. The immersions are controlled by internal thermostats. If you want full/half cylinder heating you will need a 2-immersion cylinder.