Water either Extremely hot or cold

Hi I moved into a new flat with the Pulsa-Coil A Class Boiler and unfortunately taking a shower is quite a nightmare as the water is extremely hot. There is no middle point and it is quite intermittent as well as the water sometimes turns cold suddenly.

The headertank was empty so I filled it to the correct water level (presumably this tank has been empty for a long time.

Any idea if this has an easy fix and if not how much a repair would cost approximately?

Thanks

Make sure the unit is full.
Check the tank again.
Water going hot could be a sensor problem
A DHW pump problem
Or even an ACB main board problem.
Does the water go hot & cold at your taps?
If it does then you have a PC A class fault.
But if only the shower is going hot & cold.
Then a faulty shower (thermostat)
Mike

Hi Mike, many thanks for your reply.

We do got this with all the taps. So when we use the hot water, it's extremely hot and it is not possible to regulate because if we turn the tap towards the cooler side it just turns cold. There is not really a middle point.

What is a PC A class fault?

As I put in my post.
If it is all hot water outlets.
Then you have a fault on your PC A class.
Mike