Excessive use of electricity

Hi - I have a Pulsacoil A class PC145 fitted in a tenanted apartment. In May 2019 I had a relay and base replaced as the economy 7 had stopped working, and it was diagnosed as a burnt out relay. The tenant has contacted me to say that since the repair her electric bills have gone up massively, and the units used have gone up considerably. My question is could something from the repair have caused this? There are two external switches on the wall out side the boiler housing, these are both switched on, one lights up during the economy 7 hours, the other is constantly on, to power the boiler I believe in case boost is needed. The light on the boiler which indicates faults is off, so no fault showing. She sent a video clip of the boiler ‘running’ during the day, which she said happens intermittently, and is a bit noisy. It’s hard to judge because she talked over the video clip. Other than this the boiler is Woking fine
This could be a coincidence and the electric company or meter could be at fault, but it did coincide with the repair so just trying to diagnose at the moment.
Any help or opinions would be greatly appreciated..

When they say the units have gone up is that off-peak on-peak or both? One possibility is that the off-peak element has blown (might have taken the relay with it). This would mean that the unit is being heated by the off peak boost only, although I assume that the boost should only activate when the button is pressed. It will stay on until the next off-peak session according to the manual. Do they have a SMART meter so they can see when the unit is using electricity or observe the units used readings. I would switch the boost isolator off and see what happens. Regards Murray

Thanks for the reply mmartin. The boost is not on, and as far as I can tell (not visited the apartment due to current situation ), the system is heating the water through the night as normal. Are the units split in to on & off peak on the bills? If so, I will ask the tenant to check. I have never had or used on/off peak electricity so I am not familiar with it. My gut feeling is this is a Scottish power issue and not really a boiler issue, I just wanted to put this out there to see if anybody knew of an obvious cause, as it coincidentally happened around the time of the relay replacement. The tenant is monitoring the meters, and the usage, and is going to report back. I have asked her to turn off the economy seven for 24 hours to see if the water still gets heated, if I’m right the water should not be heated unless the boost button is pressed, is that correct?

Hi yes with economy switch off and without boost there should be no electricity used. The economy is usually setup by the supplier and the two tariffs are charged at different rates which should show on the bill as separate amounts. In the old days there were two meters but nowadays it is all done with one smart meter I understand.