Governement Center with Immigration on Chaeng Wattana road ศูนย์ราชการแจ้งวัฒนะ is not well connected by public transport. Many farang have to go there for visa issues, from Sathorn/Silom/Sukhumvit it's about 200 Baht by taxi each way.
The best way to go there by public transport is MRT to Chatuchak จัตุจักร = BTS to Mor Chit หมอชิต and then bus 52 to Pak Kret ปากเกร็ด which drives past, however still a km walk from main road or mocy taxi for 20 Baht.
Update: bus 166 from Victory Monument NW corner is the most convenient by my standards public transport to get there and away.
Detailed times of my last visa extension on Thursday 20.11.2014:
11:39 MRT Klong Toey entrance
11:42 MRT Klong Toey platform
12:13 wait for bus on Pahonyothin road
12:18-43 bus 52 to Government center
12:43-58 walk to immigration (no need to haste, lunch break 12-13)
13:25-50 queue (7 before me)
13:50-55 sit at table with officer
13:55-14:21 wait to get passport back
Additional information that's not on the web: you have to sign all photocopies of your passport pages, they ask for your phone number (write either in "reason (s) for extension" or under the picture, I once again used a picture that is over a year old and visibly smaller than the field*, last time they scrutinized my address so this time I checked in my rent contract (similar for arrival card at airport, they pay attention to the address).
*I have several left from Vientiane, you need different sizes for different forms, but so far no problem with pictures that are about 5 mm smaller in each dimension than required.
But now to the subject of this post: the bus station. It's not on current Bangkok Bus Guide (thinknet 99 Baht) or on the internet.
Government complex is that vast that they have a free shuttle bus:
The bus terminal has an overview of lines 66, 114, 166, 505 and three more without number. However, only line 66 and 166 seem to actually stop there. I asked for line 505 (Lumpini - Government complex, that would allow direct access from Silom/Sathorn, but this line does not stop there).
has these two lines (66 and 166) with government complex as destination.
For line 166, there is even a timetable posted:
some websites with useful information (maps and transport options):
A friend went on Thu 12jan2017 morning, taxi from Mor Chit BTS 120 Baht, taxi back 140 Baht.
I went on Fri 13jan2017.
11:58-12:31 bus 74 for 9 Baht from Bon Gai to Victory Monument
12:48-13:20 bus 166 air for 18 Baht from ViMo to Government Complex (via expressway), there are two lines 166, some go to Pak Kret and do not pass GoCo, read their sign in Thai or ask.
(walk to GoCo, copies in underground, fill out form)
13:46 get queue number, 20 waiting
14:18-20 at counter
14:50 passport back
Update 23jan2018: taxis asking for 200 to 300 THB between GoCo and Mor Chit BTS: https://sawatdeenetwork.com/v4/showthread.php?19479-Transferring-stamps-to-a-new-passport
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