I have a 9 zone rainbird system, controller and valves. The valves are 15 years old. I recently had to replace a valve in zone 2 as it would not run. The sprinkler valves are set in groups of 3. one wire feeds the group. The groups are (1,2,3),(4,5,6),(7,8,9). Zones 1,2,3,6,7,8,9 operate normally. Zone 4 and 5 run when either 4 or 5 run from controller or in manual mode. Any ideas why these two zones would run together. This causes low pressure. PS I am in the progress of finding valves 4,5, and...