UK Immersion heater timer

wunatey · Dec 7, 2020

Hi
I have a Horstmann e7bx water heater boost controller for my immersion heater which I want to replace with a timeguard trtd7n timer which is suitable for dual element ,the only problem is that the new timer has only got 5 connections and old one has 10,is this possible or do I have to get another timer with the 10 connections?
Thanks

Avo Mk8 · Dec 7, 2020

The two controllers you mention are designed to perform slightly different functions.
My understanding is the e7bx you have is connected to both your normal rate daytime supply, and also your cheap rate supply, and provides the ability to manually switch immersions and give a boost function. It does not itself contain a timeswitch but relies on the meter cheap rate timeswitch.
So daytime rate and night rate supplies in, and connections to the immersions out.

The proposed replacement is itself a timeswitch, and can control two immersions, but it only has one permanent supply in.

It depends on your supply and billing arrangements as to the viability of the swap. You would need to connect the new timeswitch to your normal rate supply for the clock to run all the time, so the question is - if you consume power during the cheap rate period from your full rate supply, are you charged at the lower rate? In which case you could wire the new timeswitch thus, and ensure the clock 'on' and 'off' periods are within your suppliers time periods.

Then you will have a live cheap rate supply cable that now has nowhere to go in the new timeswitch!

Sorry for the verbose reply!

wunatey · Dec 7, 2020

Thanks for taking the time to reply,on the consumer unit their are 3 supplies,1 for storage heating,1 for convectors and 1 for the immersion,so I take it that the cheap rate would apply to the storage heating and the immersion,from that I can take it that if I want a permanent supply for the timer it would be at the more expensive rate,I believe you can get one with the 10 connections that can be connected straight to the E7BX but am not sure which one it is.
Thanks again

Dartlec · Dec 7, 2020

wunatey said:
Thanks for taking the time to reply,on the consumer unit their are 3 supplies,1 for storage heating,1 for convectors and 1 for the immersion,so I take it that the cheap rate would apply to the storage heating and the immersion,from that I can take it that if I want a permanent supply for the timer it would be at the more expensive rate,I believe you can get one with the 10 connections that can be connected straight to the E7BX but am not sure which one it is.
Thanks again

Usually, Economy 7 tariffs apply to all circuits from 12-7 (or whatever the local version is), so that anything running overnight like a washing machine takes advantage of the cheap rate. The specific cheap rate circuits to storage heaters etc. are hardwired just to ensure they only work when the meter is in 'cheap rate' mode.

If that's the case, then the new Timeguard would work as long as the timer was set so that the off peak load was only active during the 'cheap' rates, but you'd be relying on the Timeguard timer, not the meter.

You'd also need to safely isolate the other off peak cables in the current timer, since they would become live at the same time.

Is the existing Horstmann faulty? (You can still get them) or is there another reason for changing it to the new one?

Generally the simplest setup I've found for E7 immersions is for the lower (off peak) immersion to be wired directly from the off peak supply via a DP switch which is usually left on and will heat up only when the meter is in cheap rate.

Then either another DP switch for 'boost' mode, or if preferred, a boost timer, which shuts off after 30-60 minutes to avoid forgetting to turn it on.

Normally, the only time a combined timer/controller with connections for both immersions is needed is if there is only one permanent live feed to the immersion cupboard, so that the cheap rate immersion has to be switched to match the cheap rate times.

Hope that hasn't confused you further...

wunatey · Dec 8, 2020

Immersion Heater

wunatey said:
Thanks for taking the time to reply,on the consumer unit their are 3 supplies,1 for storage heating,1 for convectors and 1 for the immersion,so I take it that the cheap rate would apply to the storage heating and the immersion,from that I can take it that if I want a permanent supply for the timer it would be at the more expensive rate,I believe you can get one with the 10 connections that can be connected straight to the E7BX but am not sure which one it is.
Thanks again

Dartlec said:
Usually, Economy 7 tariffs apply to all circuits from 12-7 (or whatever the local version is), so that anything running overnight like a washing machine takes advantage of the cheap rate. The specific cheap rate circuits to storage heaters etc. are hardwired just to ensure they only work when the meter is in 'cheap rate' mode.

If that's the case, then the new Timeguard would work as long as the timer was set so that the off peak load was only active during the 'cheap' rates, but you'd be relying on the Timeguard timer, not the meter.

You'd also need to safely isolate the other off peak cables in the current timer, since they would become live at the same time.

Is the existing Horstmann faulty? (You can still get them) or is there another reason for changing it to the new one?

Generally the simplest setup I've found for E7 immersions is for the lower (off peak) immersion to be wired directly from the off peak supply via a DP switch which is usually left on and will heat up only when the meter is in cheap rate.

Then either another DP switch for 'boost' mode, or if preferred, a boost timer, which shuts off after 30-60 minutes to avoid forgetting to turn it on.

Normally, the only time a combined timer/controller with connections for both immersions is needed is if there is only one permanent live feed to the immersion cupboard, so that the cheap rate immersion has to be switched to match the cheap rate times.

Hope that hasn't confused you further...

Thanks again for taking the time to reply,the only reason I am changing the switch is that, I only need the hot water from the immersion in the morning,it only takes about an hour to heat the water and I do not want to have the immersion on the whole night just to get hot water in the morning,the problem with this switch is that it does not have a timer on it,it has a boost timer but that has to be switched on manually which means I have to get up early to switch it on,go back to bed then get up an hour later,is their another solution to this, other than changing the switch?
Thanks again

Dartlec · Dec 8, 2020

wunatey said:
Immersion Heater

Thanks again for taking the time to reply,the only reason I am changing the switch is that, I only need the hot water from the immersion in the morning,it only takes about an hour to heat the water and I do not want to have the immersion on the whole night just to get hot water in the morning,the problem with this switch is that it does not have a timer on it,it has a boost timer but that has to be switched on manually which means I have to get up early to switch it on,go back to bed then get up an hour later,is their another solution to this, other than changing the switch?
Thanks again

OK, there are ways of doing what you want - though not with the existing timer. It would be possible with the new one, with some adjustment.

Firstly though, if your tank is well insulated, once it has heated up to the set temperature, it uses far less power to maintain the temperature (when it's not being used) - so you may not save as much as you expect having it only on for 1 hour rather than the 7 - How much will depend on your setup, but it will be a lot less than 6/7th of the total. If you have a smart meter then it might be worth checking.

Factoring in the price of a timer and installation etc, the savings may not pay for the work for a while and good insulation on the tank may be a better investment in terms of saving money.

However, setting that aside, there are a couple of ways of achieving what you want. This assumes you currently have two feeds to the existing timer in at your cupboard, a permanent feed from the normal CU that is always live, and an off peak feed from the off peak CU, that only becomes live at 12-7(ish)

1. Use the new timer you have, using the permanent live feed, to run the lower immersion only for an hour, just before you usually wake up. In this case, the off peak feed in the existing timer will need to be terminated safely but not connected to the new timer as it will not be used.

2. Separate the feeds in the cupboard - and set up a suitable timer on the off peak feed so that it runs for an hour at the time you want, with a simple switch for the "boost" top immersion. The only issue with this is that you'll need a timer that can function with battery backup, as the live feed to it will be off for 17 hours. The benefit is that it can only ever come on at 'cheap rate' times, even if the timer gets out of sync.

There may be other ways, with smart tech, etc. but they are probably more complicated and expensive than the situation demands.

So short answer: The only way of doing what you want is to put in a timer that you can change to come on only for an hour, during the off peak time. It can be done with the new timer you have bought, but if you are at all unsure about the connections and identifying which is which or isolating, then find a local electrician who shouldn't take more than an hour to swap things out properly.

wunatey · Dec 8, 2020

Dartlec said:
OK, there are ways of doing what you want - though not with the existing timer. It would be possible with the new one, with some adjustment.

Firstly though, if your tank is well insulated, once it has heated up to the set temperature, it uses far less power to maintain the temperature (when it's not being used) - so you may not save as much as you expect having it only on for 1 hour rather than the 7 - How much will depend on your setup, but it will be a lot less than 6/7th of the total. If you have a smart meter then it might be worth checking.

Factoring in the price of a timer and installation etc, the savings may not pay for the work for a while and good insulation on the tank may be a better investment in terms of saving money.

However, setting that aside, there are a couple of ways of achieving what you want. This assumes you currently have two feeds to the existing timer in at your cupboard, a permanent feed from the normal CU that is always live, and an off peak feed from the off peak CU, that only becomes live at 12-7(ish)

1. Use the new timer you have, using the permanent live feed, to run the lower immersion only for an hour, just before you usually wake up. In this case, the off peak feed in the existing timer will need to be terminated safely but not connected to the new timer as it will not be used.

2. Separate the feeds in the cupboard - and set up a suitable timer on the off peak feed so that it runs for an hour at the time you want, with a simple switch for the "boost" top immersion. The only issue with this is that you'll need a timer that can function with battery backup, as the live feed to it will be off for 17 hours. The benefit is that it can only ever come on at 'cheap rate' times, even if the timer gets out of sync.

There may be other ways, with smart tech, etc. but they are probably more complicated and expensive than the situation demands.

So short answer: The only way of doing what you want is to put in a timer that you can change to come on only for an hour, during the off peak time. It can be done with the new timer you have bought, but if you are at all unsure about the connections and identifying which is which or isolating, then find a local electrician who shouldn't take more than an hour to swap things out properly.

Once again thanks for your time,I think I will go with getting an electrician to change it over ,I will let you know how I get on,as it is not urgent, I will leave it until this covit is cleared up.
All the best and stay safe.

GaryMac · Oct 19, 2021

I have a Horstmann Electronic 7 timer switch in my kitchen which is faulty and I want to replace. However, I no longer have Economy 7 or off-peak supply, just standard rate. The timer is only for my immersion hot water heater (3kw) which I want to programme to come on at different times of the day or boost when required. What is the best recommended switch to buy, preferably close to the size of the Horstmann to limit the redecoration required

Avo Mk8 · Oct 19, 2021

GaryMac said:
I have a Horstmann Electronic 7 timer switch in my kitchen which is faulty and I want to replace. However, I no longer have Economy 7 or off-peak supply, just standard rate. The timer is only for my immersion hot water heater (3kw) which I want to programme to come on at different times of the day or boost when required. What is the best recommended switch to buy, preferably close to the size of the Horstmann to limit the redecoration required

You may know the Horstmann timer you have, sorry had, can be linked internally (joining terminals 4 & 5) to just operate one immersion with all functions available for the single immersion. Or maybe it's wired like that already.

So buying another Horstmann might be a simple solution (new best price ~ £60)

GaryMac · Oct 19, 2021

Avo Mk8 said:
You may know the Horstmann timer you have, sorry had, can be linked internally (joining terminals 4 & 5) to just operate one immersion with all functions then available for the single immersion.

So buying another Horstmann might be a simple solution (best price ~ £60)

The Horstmann I have is designed for use off-peak, which I don’t have. I’m not sure what you mean by one immersion as I only have one immersion heater, but the biggest issue is that the Horstmann only allows me to program one one/off cycle, when I would like multiple on/off cycles at various times in the day. The horstmann was installed when I had an eco7/off-peak option which has since been removed

Avo Mk8 · Oct 19, 2021

The current Horstmann electronic 7 has three on/off periods per 24 hours, and it's not exclusively for off-peak. If you need more than 3 pre-programmed on periods during the day, I agree you will need a different unit.

A typical hot water arrangement was to have an immersion heater at the bottom of the tank, and another half way up. The bottom one would be using off-peak, and the upper one used for a boost (so you would only ever get half a tank of hot on 'boost').
The Horstmann is designed for the twin immersion situation, but with one immersion you can still use it as a conventional timer.

Mikegh · Oct 19, 2021

Didn't realize there was 2 types there

A basic boost model with 2 supplies and the timer+boost model

Can you link the outputs on both types for timed/boost control of a single heater, wouldn't be that common a requirement though would it?

Mikegh · Oct 19, 2021

Avo Mk8 · Oct 19, 2021

Mikegh said:
Didn't realize there was 2 types there

A basic boost model with 2 supplies and the timer+boost model

Can you link the outputs on both types for timed/boost control of a single heater, wouldn't be that common a requirement though would it?

The "electronic 7" (which I used to have in our property!) has a single supply in, and is configured to drive 2 immersions but ensures that both can't come on at once (obviously!). The instructions include the option to link the off-peak and boost immersion output connections together, so all the features can be available for one immersion.

It may be that GaryMac's timer was an older version than the current model above

The E7BX has separate incoming supplies for off-peak and normal
Ie two supplies (off-peak and day rate) into one single immersion:

The Economy 7 Quartz has just one supply input, as per the electronic 7, but seems to be based on 'mechanical' timers:
Used for one supply to feed two different immersion heaters normally.