If you live in ‘The Green” in Brighton then you will find this is a common complaint.
Sooner or later it will happen to you. You will start to observe dry patches in your lawn and it will look like your retic is lacking pressure.
I remember the first time I was called out to look at one of these situations I was complete puzzled as to what was causing the issue. I ended up ringing Total Eden who install all the new systems in the area and discovered that there is an inline filter right next to the master valve that regularly gets clogged up with mineral deposits from the bore water.
I removed the filter, cleaned it out re-installed it and the difference was huge. You can see a dirty one above.
If you want to do this yourself then you can follow this guide here that was recently uploaded to the Brighton Intranet. Its worthwhile doing this procedure at the start of spring and halfway through summer to ensure all is working well.