diff -r db997a04fde3 -r 4f34271cf1e7 thermferm/server.c
--- a/thermferm/server.c	Tue Aug 05 16:24:17 2014 +0200
+++ b/thermferm/server.c	Tue Aug 05 21:33:06 2014 +0200
@@ -1028,7 +1028,7 @@
 	unit->idle_rangeH = 1.0;
 	unit->idle_rangeL = -1.0;
 	unit->prof_started = (time_t)0;
-	unit->PID_err_old = 0.0;
+	unit->PID_err_old = unit->PID_I_err = 0.0;
 
 	if (Config.units == NULL) {
 	    Config.units = unit;