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My new home has a Total Heating Total Control (THTC) system. How do they work?

  • 15 September 2022
  • 57 replies
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Hi all,

 

I’ve just come here from the MSE forum having been told that the meter system for an aberdeenshire council rented property I will be moving into soon is THTC.

This huge bundle of cables and boxes is truly terrifying to me. I’ve been looking at things regarding economy meters and THTC on the internet tonight and it all means absolutely nothing!

 

Add to that, the solar panels on the roof and it just becomes an even bigger mess. Apparently Octopus are the current supplier...

 

So I was wondering if anyone can help me understand this whole system before I move in in a couple of weeks time. Especially regarding how and what gets replaced to convert it to a (hopefully!) simpler smart meter system.

Most importantly, what do I do when I move in?

 

Thank you in advance.

 

Officer_Crabtree

57 replies

Emmanuelle_OVO
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Hi @Officer_Crabtree,

 

Welcome to the OVO Online Community.

 

Total Heating Total Control (THTC) systems are more complex that most Economy 7 set ups, when you contact Support to set up your account they will discuss your options in more detail. We have advise in these similar threads which you might find helpful:

 

 

Here is a great guide about what to do when you move into a home supplied by OVO Energy: 

 

 

With your Solar Panels you’ll need to contact Octopus to set up your Smart Export Guarantee. 

 

You can book in a smart meter through your online account once you have set up your new account with OVO. 

 

Hope this helps. 

Renewable Energy? Big Fan.
Blastoise186
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Unfortunately, THTC setups are also a nightmare to migrate to Smart Meters. There’s only one known S1 Smart Meter capable of handling it

Securing energy by zapping security bugs... For that is The Blastoise Way!
O
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Thank you both @Emmanuelle_OVO and @Blastoise186.

 

So having had a bit more of a read it seems like the only current options for supplier are OVO or SSE, if that’s correct? Apart from the one strange incident of EDF… and here with octopus.

 

The biggest problem for me is I’ve never had or even seen this heating system before, so I’ve no idea on how any of it works.

Therefore I’ve no idea on if I should try and get the meters switched to economy 7 or 10 or try and get a single rate meter installed. Then again, I don’t even know how to take a meter reading from this setup. I seem to remember there were 2 different KWh numbers on the digital meter.

Hopefully I can get back there later today and see it in more detail now that I know what the system is even called!

 

Re; solar panels. I’ve yet to hear back from the council housing officer, but I believe that the council get the money from the SEG. I was told over the phone that SSE have a contract with the council for that.

 

Thank you once again!

 

Edit: Just read on the MSE forum that E7 in scotland is 8.5 hours. Is that true?

M
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Your landlord must provide you with instructions for operating the system. A smart meter will be the very least of your concerns when you move in.

Eon and EDF customer. Don't think smart meters are worth the expense.
O
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Thanks @meldrewreborn 

There were a pile of books in the corner of the kitchen, I had a quick flick through and most were about the storage heaters. Hopefully I can bring them to my current place tonight.

 

Thanks once again!

Blastoise186
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No worries. It’s probably worth mentioning that very few suppliers are actually capable of properly handling THTC setups and the last time I checked, Octopus didn’t seem to be one of them. I know OVO is planning to support them as part of the SSE to OVO Migration, but I’ve not asked for a status update in a while.

Sorry to bother you @Tim_OVO but has there been any progress on that?

Securing energy by zapping security bugs... For that is The Blastoise Way!
Blastoise186
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By the way @Officer_Crabtree , it’s really, really important that you know how storage heaters work. If you get things badly wrong, it can end up costing you hundreds or even thousands of pounds in wasted electricity.

SSE has guides for this which you can find at https://sse.co.uk/help/electric-heating/electric-night-storage-heaters . I definitely recommend checking them out. The information at https://sse.co.uk/help/electric-heating/other-two-meter-tariffs is also relevant, as it may help you to better understand how THTC works.

Because those pages might cease to exist in the near future, I’ve also created a permanent snapshot of them and submitted those to the Internet Archive. They’ll be available soon!

Securing energy by zapping security bugs... For that is The Blastoise Way!
O
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Thank you so much @Blastoise186, you’ve been a great help so far!

 

I’m on my way to the new house soon to pick up keys etc so I’ll having a good look at the meter system whilst there and I’ll pick up the mountain of instruction books whilst there.

 

I was told today by the council that I have to register with SSE first regardless of who I would want to switch to, as the council has some sort of contract with SSE regarding all their properties.

What I’ll probably do is phone up the SSE complex heating team and see what they can do to help, especially regarding opening readings. Then I’ll phone up https://www.scarf.org.uk/ and try getting some help from them regarding keeping the current meters for now or changing them out.

Blastoise186
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As promised!

https://web.archive.org/web/20220916145932/https://sse.co.uk/help/electric-heating/electric-night-storage-heaters

https://web.archive.org/web/20220916145959/https://sse.co.uk/help/electric-heating/other-two-meter-tariffs

These are permanent links. Even if the SSE site itself changes or gets closed down, these archived snapshots will still work.

I’ve also gone ahead and uploaded a few other related pages to the Internet Archive as well. If you’re browsing anything on there and run into a page it hasn’t captured yet, please feel free to hit the Save Page Now button on the error page and the Wayback Machine will grab it immediately. It’ll become available in the archive usually within 30 minutes.

Securing energy by zapping security bugs... For that is The Blastoise Way!
O
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Here’s what I saw in the fuse boxes when I got back in their last night.

I thought with THTC things like your electric shower were on the off peak rate 24/7? I’m certainly no expert, but it seems to be on the same circuit as everything else if its in the same box as the oven etc…

Does that then make this economy7?

 

No idea if this has any real relevance but the RTS meter has 6 cables coming out of it.

The white analogue meter has moved so I presume that is the standard system that is always on the peak charge? However, that means the grey digital RTS meter must be for heating, a meter for electric storage heaters that was installed all the way back in 2004 must SURELY have recorded a higher use than 16359KWh?

M
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The fuse boxes look brand new - only installed in Aug 2022.  So might the Council be able to get the engineer back to tell you how it all works?

Is it possible that the system has been updated due to the imminent demise of THTC?

The council are the landlord and they are responsible for updating the system to deal with the demise of THTC.

you though are responsible for the bills in the meantime so I’d get on their case - the Council that is.

Eon and EDF customer. Don't think smart meters are worth the expense.
O
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Hi Meldrew, all the fuse boxes are brand new, PV system was installed just last year. It really does seem like the council knows what’s going on. The problem is, absolutely everyone is closed for 3 days now…

First I’ll try SSE, then scarf and finally the council. This needs sorting out as soon as possible. The mountain of insctruction manuals aren’t all that much of a help, at least they tell me how to operate the digital controls on the heaters.

 

I did manage to snag some bills from the letterbox. I believe 2 MPANs is indicative of THTC??

More evidence of it being THTC?

 

Thank you all.

M
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Do the bills indicate Octopus as the supplier?  Its no problem but its standard that you have to sign up with the outgoing supplier first - so that could be Octopus.  It doesn’t prevent you from asking questions here as far as I’m concerned. 

 

Water heating for a storage cylinder is usually set to be on Off peak at whatever times they operate.  If you can post the top three boxes from your supply number I might be able to advise you of the times of the off peak. If the shower has its own internal heater then it has to run from the peak supply, otherwise you’d often have cold showers!

Eon and EDF customer. Don't think smart meters are worth the expense.
O
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Thanks @meldrewreborn,

 

Yes, octopus is the current supplier. Just for ease though, I’ll try and go straight with SSE as its their metering system.

 

It is an electric shower, I’m sure I read somewhere that THTC meters had a 24/7 off peak system for showers, heated towel rails, panel heaters and maybe washing machines?

 

Wasn’t too sure what to block out the first time round, hopefully this will help.

 

The one thing I’m really angry about though is 2 standing charges.

 

Thanks once again!

M.isterW
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Updated on 14/06/24 by Shads_OVO

 

Update on RTS shutdown:

 

As part of the RTS Project development, we are really happy to share with you our progress:

 

As you may be aware, the RTS signal that instructs some of our meters when to move to the “Off Peak Period”  will be closing down soon and we need to arrange for all of our RTS customers to have a meter exchange so they don’t lose any of their meter functionality.

 

The RTS signal will end for our customers on 30 June 2025. The period between 1 July - 30 September 2025 will then be used to close-down the RTS signal and allow us to manage any unexpected customers impacted.

 

After a very successful pilot, from the 17th June 2024 we will begin writing to our Economy 10 RTS customers to invite them to call us to arrange for their meter exchange. 

 

We are continuing to work at pace to enable the same solution for the majority of our other RTS customers and our aim is to begin writing to these customers in Aug 2024. 

 

We will continue to update you on our progress.

With THTC you have two meters that are charged at different rates. One meter (the more expensive one) is used for lights, cooking, normal sockets etc. That's everything in the consumer unit in your third picture.

 

The other meter is a cheaper rate and is for the stuff in the other two pictures. The storage heaters should be controlled by a radio switch. This means they should come on and off automatically and the timing is weather dependent. The water heater and panel heaters (it looks like you have three of these) are also on the cheap rate but are available all the time.

 

You have solar PV but it only feeds the stuff attached to your higher rate meter. It doesn't supply electricity to your heating.

 

Octopus doesn't support THTC so I've no idea how your system is working. I assume the radio switch is still receiving a signal to switch the storage heaters on and off. Your bill indicates that Octopus have the cheap rate meter on a two rate tariff but they're charging all the use at the lower rate. If you're happy with that and your heating is working I'd probably stick with it. OVO are supposed to be closing down the THTC radio signal next year so the system will have to be changed soon anyway.

1992 4 bed detached house. Solar PV + battery, Zappi EV charger, Mitsubishi Ecodan ASHP and i-life2 fan assisted radiators.... No gas 😊
O
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Thank you so much @M.isterW!!

I still don’t fully understand THTC (and probably never will!), but that has really helped.

 

One thing though, I’ve got a manual for a panel heater. The thing is there aren’t any in the property. the “OP” seen in the photos of the consumer unit seems to mean off peak.

Only the 3 dimplex quantum heaters have these. The manual for them says to turn on both switches, but doesn’t actually explain what they do.

 

Here’s my guess; the unmarked switch is for the “boost” function, and therefore draws from the standard peak meter? The “off peak” switch is for use of the overnight THTC function to charge them up. Why you would need to have both switches on for use is beyond me.

 

Remember the days of open fireplaces…...

M.isterW
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The way your system appears to be wired up, only the stuff in the 3rd consumer unit (shower, sockets etc) runs through the main meter (the small white one). Everything else goes through the grey box which is the radio switch and, I assume, the second meter. That means all of your heating goes through that meter. I don't know if that meter records two rates (peak and off peak) or if it's a single rate. If it's single then any time you turn the heating on it will be charged at low rate, even if you boost it during the day.

1992 4 bed detached house. Solar PV + battery, Zappi EV charger, Mitsubishi Ecodan ASHP and i-life2 fan assisted radiators.... No gas 😊
M
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The heaters might need one supply for the smart controls (think of releasing energy via fan) and the other for the main input to store the heat. 

The metering and time switch belong to the energy supply companies ( more than one) but the council may need to be notified of any change in the metering. Similarly if the wiring is changed ( by a competent person).

Eon and EDF customer. Don't think smart meters are worth the expense.
Blastoise186
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This is definitely a THTC setup. That exact Horstmann (now Secure) meter cannot be used for any other tariff type because it’s purpose built for THTC. As many of the regulars here know, I’ve been spending the last two years trying to research how THTC works so that I can understand it better and try to give better advice.

Please be advised that it looks like the Certification for it is due to expire in just under two years time and the equipment will need to be replaced at that point, while the Actaris meter appears to have already expired. As for the RTS Signal, the shutdown for it is technically beyond OVO’s control as it’s ultimately Arqiva that’s broadcasting it, primarily from Droitwich Transmitting Station, but it’s backed up by stations in Burghead and Westerglen to ensure the signal reaches properly. I was actually passing by the Droitwich one a few weeks ago and got closer to it than I’ve ever been before - and trust me, it’s HUGE!

There is another complication. If you’re in a Load Managed Area then you are required to remain on THTC unless you want to rip out all your storage heaters and put in something else that uses far less juice. Even if you go to Smart Meters, you’d still have to be on THTC. Your DNO should be able to tell you whether this applies to that supply or not if you provide them with both MPANs.

Octopus doesn’t appear to be managing your setup properly. Technically speaking, that THTC meter does have a Peak rate and any usage recorded on the Peak register needs to be charged at Peak rates, not Off-Peak. Everything on the white Actaris meter is basically standard rate and there’s no price difference between Peak/Off-Peak usage for anything going through that particular meter.

I can’t say for sure, but improper handling of the meter readings can affect industry data and make switching elsewhere more complicated than it should be.

I’ve always said that the only suppliers who are truly capable of taking on a THTC setup are/were suppliers that actually installed THTC back in the day. No-one installs it anymore and I can tell you without a shadow of a doubt that Octopus was definitely not around when THTC was first launched and by the time Octopus did launch, THTC was long gone for new installs. Technically, switching to Octopus with that meter setup should have been impossible and Octopus should have rejected the switch.

Securing energy by zapping security bugs... For that is The Blastoise Way!
O
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Thank you @meldrewreborn, that does make sense.

Just when I think I’m starting to understand it @Blastoise186 comes along and scrambles my brain!! 😊

Interesting Re; the load managed area and THTC smart meter, I tried phoning SSEN, naturally everything is closed down for the bank holiday! I’ll try again tomorrow.

 

Sorry that I’m asking so much, but does anyone from OVO know if there is anyone currently on THTC with a smart meter?

Blastoise186
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It gets worse. While this is theoretically unlikely to happen, if the RTS Signal fails while you still have the current setup, your THTC Meter will be jammed in whatever state it was in after the last successful control signal was received before the failure.

This will either mean your storage heaters are left jammed on and you get a really hot house, or your house turns into an ice cube when the storage heaters fail to activate.

There is currently only one known model of Smart Meter that is capable of handling a THTC setup. Ironically, it’s from the same company that manufactured your THTC Meter, Secure. To make things worse, it’s a SMETS1 too...

I can’t get to their website right now though as the TLS Certificate for it has been revoked and erm… Well…

Yeah…

If I try to get Bitdefender to step out of the way temporarily, Chrome will only block me anyway for the same reason. But then again, it was issued by GoDaddy so I’m not surprised because GoDaddy is just terrible! XD

There is no-one currently known to be using a THTC capable Smart Meter that we’re aware of.

Securing energy by zapping security bugs... For that is The Blastoise Way!
O
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Thanks @Blastoise186, looks like its a wait and see situation. How long those of us with RTS meters can wait for seems to be a guessing game...

Blastoise186
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No worries.

I wouldn’t recommend trying to talk to Octopus about any of this, purely because there’s a very low chance they’ll actually have anyone who knows about this stuff and I can’t reasonably foresee them having anything equivalent to SSE’s complex heating team. I’m supplied by OVO these days, but I used to be an SSE customer until just after OVO took over. You could say I basically jumped the queue and switched pretty quickly, since I knew it was going to happen eventually anyway! Pure luck has occurred in the two years since which has put me in a rather… Fortunate position.

I’ve only got a bog standard Single-Phase Single-Rate supply myself, nothing fancy other than having a SMETS2 Smart Meter installed by OVO after they managed to (accidentally!) brick the SMETS1 meter that SSE originally installed.

As it also happens, the only suppliers that seem to have complex heating teams who can give the advice you’re after, are those that were known to support THTC which basically means (from memory!):

  • SSE
  • EDF
  • Scottish Power

I don’t know of any other supplier that offered it. Either because they’re gone or because they got took over and the buyer didn’t support THTC at all. Technically, OVO is too young to have had THTC support, but the takeover of SSE’s retail division has changed the game.

The ultimate answer about the wait is… How long is a piece of string? I can definitely say there are plans to migrate properties like yours, but it’s a complicated process!

Securing energy by zapping security bugs... For that is The Blastoise Way!
O
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Thank you so much @Blastoise186, I’ll try and keep you somewhat in the loop and can hopefully end up providing the solution to anyone else struggling with THTC in the future.

M
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Does the new system have to be equivalent to the old?  I don’t see that as being possible. Surely the only sensible solution is economy 7 and Octopus should be able to handle that - If they can get their hands on an economy 7 smart meter.  Other forums suggest there is a supply problem at present.

its a possibility that a charge for changing the meters might be proposed, but if the meters are out of certification, then that might not be an issue.  There must be lots of customers with this sort of issue, I doubt that you’ll be the first they’ve dealt with.

 

Eon and EDF customer. Don't think smart meters are worth the expense.

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