[cheshired5]

As suggested earlier, a £50 regas at a high street centre could be a cost effective route to diagnosis.

If you have a leak, they can't regas so won't charge.
You then know that your pressure sensor is most likely working and doesn't need replacing so your money can go towards fixing the leak.

If you don't have a leak and it holds good pressure using the garage pressure gauge but your pressure reading is still duff, your pressure sensor is faulty and there are plenty available for reasonable money.