Hi @Bren1947 , if the only change has been the heaters themselves, there must be something different about their wiring, unless these are not storage heaters of course. The previous wiring would have had two circuits, one for your off-peak power and the other (boost) for on peak. 
Do you have any photos, particularly of the cabling?

Thank you. The new heaters are oil filled radiators.  It was an electrician who installed them. I have contacted him.

Hi @Bren1947,

It seems our forum volunteer has already given some good advice here. Hope it’s been helpful. Please let us know how you get on.

@BPLightlog My electrician has been in touch and I need to program the new heaters in order for them to function on the THTC system. Hopefully, I will soon be free of THTC as OVO are supposed to be removing the second meter and at the same time installing a smart meter on 30th September. Thank you for your help, 1947 may have been a good year for wine (or not! )but not for understanding the complexities of trying to keep warm and avoiding big bills!! 

Yes @Bren1947 , not everything is as easy as it should be. Glad we could help - a little. There are several here with quite a knowledge in different areas so do pop back if you think we can help at all. 
 

NB~ it looks like 1947 was a decent year for wine 

[ot]

1947 was a truly ‘vintage year’. Every five or ten years, I used to look up the wines my father laid down for me when I was born to see whether it was time to drink them. At one stage, the St Emilion was reported to be ‘drinking well’,  while the Nuits-St-Georges was ‘beginning to show its age’. I took the hint, so the wine didn’t last the year, but I soldier on ...