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

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.

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.

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!

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!

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…...

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.

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).

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.

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?