A: It could be a faulty relay board or faulty flow valve there is no way to know for sure.
However our experience is, if the service light comes on then it’s most likely to be a faulty relay board.
No lights at all then it’s probably the relay board
If it’s low pressure light is on then it could be a faulty the flow valve or relay board.
If you are unsure start with the relay board, this is the more common fault.
On a few occasions you may need both, if you need to be certain then order both!
No lights at all then you may have a faulty transformer also check that you actually have a power supply to the shower.
To Check the transformer, there is a white plug at the top of the relay board, the blue and red wires are mains and should have 240v the black wires are from the transformer and should have 12v AC
If the transformer is OK once again, start with the relay board.
Fitting Board and valve.
Obviously turn the power and water off .
Changing the board is fairly straight forward just take notes and photos of where all the cables and plugs go as you dismantle then it should be easy to reverse the procedure.
To change the flow valve you have to remove the ‘U’ clamp on the inlet and the screw at the foot of the heating tank there is then a small tab to the right of the heating tank this is a clip you need to pull this forward to release the hook you may need to use a screwdriver or pliers to flick it forward.
The tank and valve should then pull forward enough to be able to separate them, then remove the plug from the circuit board.
Fit the two new ‘O’ rings supplied and then push the tank and valve together offer the assembly back up and into place, refit the ‘U’ clamp and the screw at the bottom of the tank and make sure that the hook clippie thing is firmly pushed back into place.
Turn on water and test also check the earth wire that runs across the top of the flow valve is clear of the purge button and remember to press the purge button for 15secs to allow the heating tank to refill.