Harvey Water Softener will not recharge consistently

[BrianPh]

I have have a Harvey Water Softener Minimax M3 and it stopped working. I have had 2 engineers come out and they have put in a service kit, changed all the gears and replaced the risers. When they test it, it works fine and also when they test in automatic, but when they go and the required 375 litres goes through the system it just makes a clicking sound as if the meters are spinning but there appears to be little or no water going through it. Awe know it is not working because the water is still hard. The resin level is good. What else could be causing the problem?