Gainsborough Energy 2000x 10.8kw not heating

The things to check first are.

1 That the main valve coming into your house is fully open.

2 Then check that the valve on the line to the shower is fully open.

If these valves are not fully open then there may not be enough water
getting to your shower open / close the safety device that allows power through to the elements

Make sure that the shower head is clean and clear, that the hose isn’t kinked (this can happen just behind the hand set where it is difficult to see) also check the inside of the hose although it can look OK on the outside it could have collapsed internally

The other possibility is a faulty flow/stabilizer valve not allowing the correct amount of water into the shower.

A ruff check is to remove the shower head turn temperature control to fully hot the water coming out of the hose should be a bit more than a dribble then turn to fully cold and it should be coming out at full flow.

If there is not much difference between the two then you could have a faulty flow valve.

Carry out this check after you check the inlet valves.