Why does the off peak light come on automatically??

This happens when the off peak is switched on(boost for a bath) it does the normal routine on for an hour.sometimes less, then goes off.
Now when hot water is called for,not a lot, the pump will run to equalise the temp. and the off peak light will come on for 5mins or so.This will happen each time hot water is called for.The initial water temp is scalding for a few seconds and steaming.This only happens following an activation of the off peak use,otherwise no problem.

Does not make sense..
Have you the user book and manual?
Off peak should be on for 7 hours every night to heat the thermal store up.
The boost black button on the front of the unit is used for back up or if hot water has been used up.
Feel the big pipe on top of the unit.
If you can hold it, then the unit is not hot enough.
Mike

I am sorry Mike,i was getting my peak and off peak mixed up.
Of course it deals with the daytime boost activation,on peak time.I was thinking that if the boost is activated it stays on for anhour ave. now at times this boost light will go off before the hour is up,so if hotwater is called for afterwards does the boost come on to use up the time still available within that hour?
The boost only comes on for 5-8mins each time until I assume the remaning time is used up on the original activation.

thanks for getting back to me.

You use the off peak to heat the store up.
If you have no hot water because;
The off peak has failed / broken.
Or the hot water has been used.
Then you press the boost on the PC A class unit.
It will heat up approx the top third of the unit.
The time varies. All depends how much hot water etc there is.
Also whilst heating if you use it it will keep heating.
Once the unit has heated the top section up it will switch off.
After which if you need it the you have to press the button.
E 7 is the correct way to be heating your unit up.
7 hours half price.
But again it may only heat up for 3, 4, 5, 6 or 7 hours depending on how much has been used from the store.
You need to read the manual to see how your unit has been connected up.
Have you spoken to your neigbours to see how they use theirs etc.
Mike