Pulsacoil 2000 issues

Hi there

I recently moved into an apartment with a Pulsacoil 2000 which was drained down. As the fusebox in the apartment was incorrectly labelled, I accidentally turned the power on when the unit was empty, resulting in the red error light below the green one.

I subsequently turned it off, opened the front cover and pressed the reset button. I then filled the unit using the open tank on top, as in I filled the tank several times until it maintained the correct level.

After turning on the unit using off-peak only (I'm not sure if it is wired up correctly) I have hot water. However the circuit board flashes 7 times indicating DHW sensor failure. There is no red or green light on the cover panel.

The unit also seems to get quite hot so I have started turning it off during the day and only on at night to heat the water for the next morning.

I have been quoted £400 by Gledhill for a fixed price repair, but wanted to know if I could replace the sensors myself or if perhaps there is another fault. Eventually I intend to replace the unit entirely, but would just like to get this unit in proper order for the next year or two.

Any advice or recommendations would be very appreciated.

Thanks!

Thermal sore is to be left on.
Use E7 or E 10
It is similar to a battery, but instead of storing electricity.
It stores heat, which heats up your hot water as it goes into the unit and out again (simple terms)
The flashing lights point to a fault.
DHW sensor.
Mike
PS
If people were to add there area / location.
Offers of help etc may / could come from a local engineer.