Noisy Emersion tank!

[route66]

My heating runs on an economy 7 system. Our hot water tank and storage heaters run off this. Recently the e7 emersion heater broke and we had to have it replaced. Prior to the replacement, the tank used to make a noise during the night about every 10-15 mins for about 10 seconds, i assume during the e7 period, when the tank was filling up/heating the water.
Since being fixed, the tank has constantly made this noise again every 10-15 mins for about 10 seconds. Should it be making this noise throughout the day? We are concerned that our next electricity bill is going to be huge! We have tried to contact the plumber to ask the question but surprise surprise he is not answering our calls.
Please please advise.....

 

[Puddle]

Would get it checked,seems wired incorrectly or economy 7 control unit faulty,should only operate in the day time if on boost,if working during day,your electricity bill is going to be increased

 

[route66]

Cheers. Thats exactly what we thought.
Dont suppose you know if the switch that is connected to the e7 heater should be on or off? I cant remember what it was before the plumber came.
I should have known he was a cowboy when he didnt seem to understand what e7 was!!!