If your head swirls the water around and never seems to get it all out of the bowl, it may be time for a rebuild.
With regular use, a two-year schedule to rebuild the head is generally a good guideline.
A few hints for those of you that don't mind doing the dirty work:
1. Regular maintenance. Our monthly routine of white vinegar and oil will greatly reduce the build-up in the head and render the job much easier and cleaner.
2. Coat all rubber valves, o-rings, and seals with silicone grease. It makes a great seal and keeps the head operating smoothly and you can find it in the plumbing section at any hardware store.
3. Straight white vinegar. This will dissolve the heavy crystallized build in passages which restricts flow and will eventually block the passage. If you notice build-up in passages or hoses when you have everything disassembled, clean it out now while you have the access and remember to do your regular vinegar and oil maintenance in the future to avoid cleaning it out again!
4. Use new hose clamps. It's an easy way to cut corners to reuse the old ones, but they will leak - it's Murphy's Law. Let's face it, do you really want them to leak?
5. Vick's Vapor Rub. If you have a sensitive sniffer, or just don't want to smell what you are doing, put a dab of Vick's Vapor Rub under your nose. Yes, it really works and your sinuses will be clear all day!