PostgreSQL AFTER INSERT trigger prevents insert - postgresql

Question

I have a PostgreSQL 9.3 database. I use a log4net configuration to insert the errors in a table: log_messages.
I have a webpage that shows the errors in a nice way with charts and such.
Because I use a rather complex view this webpage is very slow, so I moved to a materialized view. My page is fast again.
Now I need to keep my materialized view in sync with my table/view. So I created a AFTER INSERT trigger on the table:
CREATE TRIGGER refresh_mv_insert
AFTER INSERT
ON log_messages
FOR EACH ROW
EXECUTE PROCEDURE refresh_mv();
My refresh_mv() is more complicated but even this simplified version doesn't work:
CREATE OR REPLACE FUNCTION refresh_mv()
RETURNS trigger AS
$BODY$
DECLARE
l_view_name character varying := 'mv_log_messages';
begin
EXECUTE 'REFRESH MATERIALIZED VIEW ' || l_view_name;
RETURN NEW;
end;
$BODY$
LANGUAGE plpgsql VOLATILE
COST 100;
When I change it to an anonymous procedure the full and simplified version do work. So it seems I have an error in the Trigger part.
I've been reading documentation and similar Q&A for two days now but I can't get it to work.
Any help is much appreciated.
Edit: Clarification
In my full trigger procedure I use a config table to store the refresh timestamp and I don't refresh within an hour.
When I enable the trigger the record is not saved into the log_messages table.
I don't know how to read any trigger errors. Where can I find them?
Here's my full code:
CREATE OR REPLACE FUNCTION refresh_mv()
RETURNS trigger AS
$BODY$
DECLARE
l_last_refresh timestamp;
l_view_name character varying := 'mv_log_messages';
l_num_new smallint;
l_refresh boolean := false;
begin
l_refresh := false;
-- check the last time:
select last_refresh, num_new into l_last_refresh, l_num_new from config where view_name = l_view_name;
-- refresh every hour
if (l_last_refresh + interval '1 hour' < current_timestamp) then
l_refresh := true;
end if;
-- refresh every 10 inserts, but not more often than every 10 minutes:
if (l_num_new > 9 and l_last_refresh + interval '10 minutes' < current_timestamp) then
l_refresh := true;
end if;
if l_refresh then
-- Reset config and do refresh:
update config set last_refresh = current_timestamp, num_new = 0 where view_name = l_view_name;
-- this line prevents the insertion of the record EXECUTE 'REFRESH MATERIALIZED VIEW ' || l_view_name;
else
-- Update counter:
update config set num_new = l_num_new + 1 where view_name = l_view_name;
end if;
RETURN NULL;
end;
$BODY$
LANGUAGE plpgsql VOLATILE
COST 100;
This trigger works because I commented the line EXECUTE 'REFRESH MATERIALIZED VIEW ' || l_view_name;