I contacted the seller and this is what he said (my warranty ran out 2 weeks ago lol)
"Thankfully the dimmer is the only problem we've ever had with these.
because the dimmer isn't waterproof, over time moisture and dirt gets inside the gaps.
snip 1 of the dimmers off, if its the dimmer that is the problem, you'll see an instant fix, it will be a lot brighter.
a lot of the time, just moving the dimmer to sit on top of the heatsink will dry it out and get it to work normally.
let me know how you go."