I agree with forkingabout, you can do some real damage to these controllers if you don't know what you doing.

However its very frustrating when even though I've diagnosed the fault (i.e lift pot on a linde) I have to get the manufactuer out to train it in. Customers are sometimes unforgiving because they decide "you don't know what your doing"
We lost a service contract recently simply because we couldn't reset the service interval indicators, even though our service work was flawless. This can hardly be fair.