THTC and RTS shutdown

Hi, I currently have the Scottish THTC (Total Heat Total Control) tariff and meter set up.  I am soon changing to a smart meter and Economy 10 tariff because of the RTS (Radio Teleswitch Service) switch off in June 2025. 

I currently have two non revenue sub meters (standard use and heating/THTC) in an annexe part of my house so that I can measure how much electricity is used there.  But I am billed on just one bill for the whole house based on readings from my main meters.

Will it be possible to replace my non revenue meters so that I can continue to measure the use in the annexe?  I accept I would need to do and pay for this privately.  I’m not sure how the current system, with separate standard and heating circuits and meters would change to a time based system with off peak and peak measurement.   Would I have to buy a single (peak/off peak) meter and route all the wires for the annexe through that meter?  Could I somehow re-use the existing meter(s)?

Howdy ​@MarkW123 !

I suspect you’ll be able to just keep using the sub-meters more or less as they are now. But you’d obviously want to grab a meter reading from them just before the engineer kills the supply meters so you have a new starting point after the upgrade work is done.

But could you show us some photos of the setup by any chance? If you’ve got wiring diagrams too, that’d be amazing.

Thanks!

Hi Blastoise186

Thanks for your swift response.  Sorry I’ve only just been able to reply.  I’m attaching photos but do not have wiring diagrams, sorry.

The first photo shows the main meters for the entire house (Std and THTC) and the consumer units for the house (excluding annexe).  So, the circuits for Storage heaters, panel heaters, showers and water tank all go through the THTC meter which has a cheaper unit rate, whatever time of day.  The other circuits (lighting, sockets, cooker etc) go through the standard meter which has a more expensive unit rate, whatever time of day.

The annexe meters are shown in next pictures.  Again, the heating, water and shower go through the THTC meter and the other circuits go through the standard meter.

My understanding of the Economy 10 tariff, that I’m forced to move to, is that the entire

electricity use is measured together but counted as peak or off-peak, depending on time of day (ie no matter what the electricity is used for).  So I’m not clear how the meters could continue to be used.  I was thinking that all the annexe circuits would have to go through a new dual (peak/off peak) sub-meter so that I can see how much is being used at each rate.   

Alternatively, I guess that if I thought the standard use electricity was not that significant I could re-use the standard meter and direct all the annexe consumption through that.  It would show total Kwh used but I’d have to come up with an adjustment to the unit rate if I wanted to charge for annexe use fairly….. 

Does that make sense?

Cheers

Oh wow, quite the rats nest you’ve got there!

I think you may just have to end up being very careful, but I’ve got one more question - this will absolutely help us figure out how to answer your question.

Is someone living in the annexe who pays you for what they use in some way?

Indeed, That’s why wiring diagram not available!

In the past we have used annexe for holiday let but not charged for electricity directly.  Just used it as guide to costs.  Now have friend staying as lodger and using meter readings to assess electricity bill on monthly basis.

Is there anything to stop me buying a dual meter and feeding everything through that?

Cheers

You can if you want to - I suspect it may be your only option.

Make sure you don’t make a profit out of this though - otherwise you get snarled up in legal red tape that you really don’t want to be wrapped up in...

Thanks, no not wanting to make profit from it.  Thanks for the advice.  Will obviously talk it through with the electrician I use.

Cheers

Hi everyone.

My elderly parents are extremely clinically vulnerable (88 and 90, numerous health issues inc COPD, heart disease and lower leg amputation). 

I know the radio signal is being switched off and I need to ring and get them a smart meter fitted. I have been holding off as they still have their heating on full time, and I couldn’t risk anything going wrong/them being without heat for even 1 day. Now it’s warming up and they will be switching the heating off soon, I am ringing up to book an engineer appointment. 

I have enclosed some pics of the set up. This meter is decades old (they are the generation that if something worked, they just plodded on with it for years). They migrated from SSE to Ovo. They have an economy 7 set up I believe with an afternoon boost to their storage heathers (all electric house, no gas). They also have an economy 7 immersion heater which gets the same overnight and afternoon boost.

My question is: is this a set up that can be switched over to smart meter or does anything have to change compared to how they have it now? I have calculated a whole previous years’ bills and bc they have the heating on for at least 7 months of the year, it is barely any different to what a single rate would cost. 

Their bills are broken into off peak rate, peak rate and heating rate (I input 3 sets of readings on the ovo website). Because they have storage heaters we need to be able to have overnight boost and afternoon boost.

Thanks for reading :)

Thanks for submitting a very clear enquiry!

One vital fact you forgot: where your parents live. The options vary considerably across the country. It’s usually enough to know the first part of of the postcode, or the nearest town if they’re in a rural area.

The big before/after difference is that there will no longer be a 24-hour heating circuit as they may have at the moment (“I input 3 sets of readings on the ovo website”).  This means that the lower rate for heating will only apply during offpeak hours, so the new arrangement will involve some changes to behaviour if your parents are to avoid paying too much for their heating. It would help to know what other heating equipment they have, if the storage heaters aren’t able to to keep them comfortable all the time.

There doesn’t appear at first sight to be anything to prevent a straight exchange of the old telemeter for a new smart meter. If the new meter is able to communicate well with the smart meter network (the ‘WAN’), it’s all a bit easier. 

I’ll be back with some suggestions when I’ve seen your reply.