This question has come up a few times. The two that are always recommended are Sutter Home & Hearth in Ballard, and Ron Swenson 206-799-0454.
Sutter (who I use for my Valor gas insert) will only service brands they sell. They get really busy this time of year so there could be a wait for service.
I have used Seattle Fireplace twice and have been very happy. I just had that same issue and a part was worn out and they replaced it and cleaned the fireplace. 206-799-0454