AT THE START OF THE SEASON, Im always a little more paranoid than usual. Following a winter of mostly overseas diving, my UK dive kit comes out of the cupboard, gets loaded into the back of the car and is driven to the site. In an ideal world, it would work as perfectly as last time I used it.
But we all know that things dont happen that way. Kit left alone has a habit of developing problems, even though it hasnt been used. Or perhaps its exactly because it hasnt been used.
Then there are all those glitches that I tolerated as they gradually accumulated the previous season. None bad enough to stop me diving, but a nuisance I had vowed to sort out during the winter. Yet, like most divers, I never got round to doing it all.
I may drop my regulators off at a dive shop for servicing. Do this and you may expect them to work perfectly first time out. But while the vast majority of dive shops can be relied on to do a good job, it is by no means a certainty.
There are sloppy service technicians about, and even the best can have a bad day. Ask any working dive guide and you will be told that the time when equipment is most likely to fail is immediately after servicing!
The bottom line is, whether because of general neglect since it was last used, lack of use, lack of servicing or recent servicing, those of us who assume that dive kit will function perfectly will eventually get caught out - and not just at the start of the season.
The regulator is the part of our dive kit most likely to kill us, so before even putting a reg on a cylinder, here are some health checks that anyone can do.

Slide the hose-protector back to examine the hose ends
Inspect for gouges, cuts and splits, especially at the ends where a hose runs into a ferrule. If hose-protectors are fitted, pull them back far enough to examine where the hoses run under the protectors.
These parts of the hoses may be protected, but they are also where damage could easily go unnoticed.
Some divers go so far as to avoid using hose-protectors for this reason. I like to get as many dives out of a hose as possible, so I prefer to use protectors and check beneath every now and then.
If you need to twist a hose-protector to get it to slide back, its usually easiest to do this while the hose is still attached to the first stage. Twist clockwise while pulling on it and the hose wont come unscrewed in the process.
If it is tight, running a little warm soapy water inside the protector can help.
If it wont budge, let it soak (ensuring that the first stage doesnt get wet inside). If it still won't come loose, pulling too hard may damage the hose you are trying to protect, so at that point I would either scrap the hose or very carefully cut the hose-protector off and fit a new one.
If a hose is damaged right at the end, the obvious solution is to replace the entire hose, but there are other ways.
AP Diving hoses come with screw-in re-usable ends. As these are designed to be unscrewed, a hose can be cut to the right length. Providing there is a little slack in a hose, you can just cut a few centimetres off the end and screw it back on.
If your hoses dont come from AP, you can also get re-usable ends from Subaqua Products.
If you do remove or fit a re-usable hose end, follow the instructions to the letter - particularly the part about the outer section having a reverse thread.
While at the upper end of the hoses, check carefully that none of the O-rings where they screw into the first stage are beginning to extrude, or were pinched when the hose was fitted. At the same time, ensure that the hose end isnt loose where it is screwed into the first stage.

A problem I have witnessed just after a regulator has been serviced arises when mouthpieces are not properly secured - either because a cable-tie has not been tightened enough, or because there is no cable-tie at all. Even if a mouthpiece hasnt been replaced, it may have been removed during a service, or the cable tie may just have stretched with age.
At the same time, see if the cable-tie has been cut so as to leave a sharp end. If it has, it can be carefully cut back further with a knife or snippers before smoothing off the remainder with a nail-file.
On an old mouthpiece, look to see if it is beginning to split just behind the cable tie that secures it to the regulator.
Also look at the lugs around which your teeth go, and make sure that those lugs are not splitting away from the rest of the mouthpiece.
If you replace a mouthpiece, fit one that is the correct size for the regulator. Stretching a mouthpiece that is too small will split it, and fitting one too large could leave a leak, or risk it falling off during a dive.

The sintered filter should be clean - look into the hole
A common cause of high breathing resistance on an otherwise correctly functioning regulator is clogging of the sintered metal filter, where the first stage mates to the cylinder valve. A bit of dried salt, a touch of corrosion and a speck of dirt can between them make a big difference.
A quick visual check is easy enough. Just look into the hole and see how clean it looks. Unless a regulator has just been serviced the sintered filter will never look perfect, but it shouldnt look corroded and dirty.
If in doubt, take a swab with a cotton bud and see how much dirt is on the outer surface. Dont rub hard enough to leave fibres on the filter.

Give everything on the second stage a waggle and see if it is loose.
Does the exhaust deflector fall off Does the diaphragm cover at the front fall off Is whatever locking mechanism is used for the diaphragm cover actually in place
A few years back I was sitting on a boat at Hand Deeps, preparing to dive with a friend who had just had his regulator serviced. He turned his air on and bits of second stage shot across the deck.
We never did find the locking-pin, and suspect that either it had not been replaced during the service, or had not been fitted fully.
It had been OK back on the dock, but during the boat ride it had bounced about enough to turn a loose cover into pneumatic ammunition.

Sucking gently can indicate whether the exhaust mushroom is faulty
Having made sure that everything is secure, and the mouthpiece is intact, check the exhaust mushroom. This is a rubber flap mushroom valve, typically just below the mouthpiece and hidden by the exhaust deflector.
Over time, a mushroom valve can curl at the edges, be damaged by grit or sand, split or even come loose. I know of one regulator that came back from a service without a mushroom. Either it hadnt been fitted, or it had been poorly secured and fell out between shop and swimming-pool.
Look through the exhaust deflector. On some regulators the exhaust mushroom is easily visible, though on others it isnt. Just try to confirm that it isnt curled up at the edges or missing.
Next, leaving the first stage sealed with a dust cap or a finger over the hole, gently suck through the mouthpiece. If any air gets in, chances are its the exhaust mushroom leaking.
Dont suck too hard. If there is a leak it will show up with a gentle suck, and sucking too hard could actually cause a leak, folding the mushroom or dislodging the diaphragm.

The second stage is just beginning to hiss as the water draws level with the mouthpiece. Cracking resistance is OK
Now we can attach the regulator to an air cylinder. Breathing off it is an obvious step, but just what should the breathing resistance be
Its difficult to assess just how easily a regulator breathes without taking it on a dive.
A simple test for most regulators is the kitchen sink. With the mouthpiece uppermost and the diaphragm lowest, slowly immerse the second stage in the water, making sure to get no water inside it.
As it gets lower, a pressure difference of just a few centimetres of water will build up across the diaphragm, enough for it to push in and let out a faint hiss of air.
With any conventional regulator, this hiss should occur just before the water laps over the mouthpiece, and brings the test to a halt. In engineering terms, the cracking resistance should be a few centimetres of water pressure.
If it doesnt crack and gently hiss, the breathing will be too tight. If it just splurges out in a freeflow, the breathing resistance is too loose.
If a regulator fails this test before taking it for a service, rinse it out with warm clean water to make sure it wasnt just dirty or sticky from lack of use. Also double-check that any adjustment knob is set correctly.

If the IP is this low, something is wrong. This cylinder was off
The next few tests are the only ones for which you need a specialised tool. An intermediate pressure gauge (IP gauge) typically measures 20 or 25 bar across the whole range.
It can either be screwed into a spare low-pressure port on the first stage, or may come with an adapter to plug into a BC or drysuit feed hose.
Most regulators have a recommended IP of about 10 bar, perhaps +/- 1 bar, though there are exceptions. Fit the IP gauge, turn the air on and check that the value is within this range, or whatever the correct value for the regulator should be.

Leave the air turned on and watch the needle for 10 minutes. If the intermediate pressure creeps up, this is a sign that air is leaking past the first-stage valve seat because it isnt closing properly.
The malady is called first stage creep or IP creep. The first stage needs attention.
If you dont have an IP gauge, the usual symptom of this is a regulator that is perfectly all right while it is being breathed from but, if it is left alone for more than a few breaths, will slowly start to hiss air from the second stage.
The IP has crept up to the point at which it pushes the second stage open.

For a basic check of hp gauge accuracy, you need two cylinders, one full and one almost empty, and a second regulator with an HP gauge that is known to be accurate.
Use the second regulator and HP gauge to check the pressure in each cylinder, then compare this with the HP gauge that is on the regulator being checked. If they disagree, one or the other is wrong.

Checking the interstage pressure
Next, take a few breaths and watch the IP gauge needle flutter down and up while youre breathing. It should dip only a few bar, and should recover as soon as you stop inhaling.
If it dips and does not immediately recover, thats a bad sign - this time that the first stage is not opening properly.
However, low-performing designs of first stage will dip further and take longer to recover.

When happy that the IP pressure is not creeping, leave the regulator on a cylinder and the air turned on overnight, especially if it has just been serviced.
Valve seats can take time to bed in, and after a few hours under pressure the IP and breathing characteristics may have changed. In the morning, check the IP again and make the other checks for creep, cracking resistance and flutter.
Doing the same overnight test with the cylinder turned off can indicate very minor leaks, as the pressure indicated by the regulators HP gauge will drop as the air in the first stage and hoses slowly leaks away.
Even regulators in the best condition are unlikely to pass this test, so it is more a question of how fast it leaks away than whether it leaks at all.

This HP swivel is leaking a mist of tiny bubbles
The most common problem with the hp gauge is a small leak where it attaches to the hp hose, or just above that at the hp swivel.
Getting it wet in the kitchen sink is by far the easiest way to identify and track down the source of small hp leaks.
If it is where the gauge attaches to the hose that is leaking, simply tightening the connection may cure the problem, but be careful not to over-tighten and strip the thread.
In general, never use more than the shortest spanner and never use the full length of the spanner for leverage.
If it is the swivel that is leaking, sometimes with a regulator that hasnt been used for a while, just getting the swivel wet and wiggling it around will cure the problem. If not, the tiny O-ring inside will need replacing.

Get it wet and look for bubbles that would reveal leaks in the first stage
This simple test is so obvious that it may seem amazing that all the other checks came first, but in fact the sequence of checks is pretty much down to whatever is convenient. Attach the regulator to an air cylinder, then turn the whole lot upside down and dip it in the kitchen sink. Let everything settle, look for bubbles and note where they come from. Then purge the second stage a few times and look for bubbles again.

A sticky high-pressure gauge has been the cause of more than one start of season out-of-air scare, causing divers to think that they had more air remaining than they actually did.
With the regulator on a full cylinder, turn the cylinder on to pressurise the regulator, then turn it off again. Gently hold the purge button so that the second stage just purges at a constant rate while watching the HP gauge needle. It should go down smoothly without sticking.